After undergoing processes such as molding, sintering, and hot isostatic pressing, MgAl₂O₄ transparent ceramics accumulate significant residual stresses inside, directly affecting the optical uniformity of the material, and even causing deformation and cracking during subsequent processing and application due to stress release. In addition, due to the fact that the hot isostatic pressing heating components are made of carbon fiber material, they can cause a certain degree of carbon pollution to the pre-fired parts under high temperature and high-pressure conditions. They are issues that must be addressed and solved in engineering applications. The annealing process has always been used in the field of metal and glass heat treatment, while the application in the field of transparent ceramics focuses more on the influence of annealing process on the optical properties. However, there is a lack of in-depth research on its influence mechanism. At the same time, removing residual stress is one of the main purposes of annealing treatment for transparent ceramic materials, and its evolution process analysis is rarely reported. Therefore, it is very necessary to conduct research on the effect and mechanisms of annealing treatment on the optical properties and residual stress. In addition, the temperature range for rapid growth of MgAl₂O₄ transparent ceramics grains can be determined, providing a reliable reference for the practical application of the material.In this paper, MgAl₂O₄ transparent ceramics were prepared by pressureless sintering combined with hot isostatic pressing treatment. The residual stress of the material was characterized by two methods: stress birefringence optical path difference and micro-Raman spectroscopy characteristic peak frequency shift. The influence of annealing temperature on the full wavelength optical transmittance and residual stress of MgAl₂O₄ transparent ceramics was mainly studied. The influence mechanism was analyzed and explained by discrete dipole calculation based on Mie scattering theory, micro structure characterization, and lattice constant calculation.When the annealing temperature is lower than 1300 ℃, the transmittance decreases mainly below 450 nm, when the annealing temperature is higher than 1 300 ℃, the transmittance of the whole band begins to decrease rapidly, and the decrease of transmittance in the short-wave band is significantly higher than that in the infrared band. The results of discrete dipole calculation based on Mie scattering theory and microstructure characterization show that it is mainly due to the scattering in different wave bands by the pores after expansion and splitting with the increase of annealing temperature. The residual stress in MgAl₂O₄ transparent ceramics is compressive stress, which shows the characteristics of uneven distribution. The residual stress first gradually decreases with the increase of annealing temperature, and after reaching the lowest point, the residual stress increases as the annealing temperature continues to increase to 1 350 ℃. However, the lattice constant is not compressed at this time, which indicates that lattice distortion is one of the main reasons for the residual stress of MgAl₂O₄ transparent ceramics but when the annealing temperature is too high, accompanied by pore expansion and secondary crystallization, the rigid extrusion of the interface structure between grain and pore is dominant.The influence of annealing temperature on the full wavelength optical transmittance and residual stress of MgAl₂O₄ transparent ceramics was mainly studied. The influence mechanism was analyzed and explained by discrete dipole calculation based on Mie scattering theory, micro structure characterization, and lattice constant calculation. The experimental results show that: 1) The influence of annealing temperature on the optical transmittance of MgAl₂O₄ transparent ceramics in whole wavelength lies in the influence of the residual pores evolution under different annealing conditions. 2) Annealing is an effective means of material residual stress relaxation, and the residual stress can be effectively characterized by the stress birefringence optical path difference and the characteristic peak frequency shift of micro-Raman spectroscopy. The residual stress first gradually decreases with the increasing of annealing temperature, and then reaches the lowest point, at last the residual stress increases as the annealing temperature continues to increase. The results of the two test methods have the same trend, but the difference is that the annealing temperature corresponding to the lowest stress value is slightly deviated, which is mainly due to the surface processing stress introduced during the grinding and polishing process of the sample surface. 3) lattice distortion is one of the main reasons for the residual stress of MgAl₂O₄ transparent ceramics, but when the annealing temperature is too high, accompanied by pore expansion and secondary crystallization, the rigid extrusion of the interface structure between grain, grain and pore is dominant. 4) The rapid grain growth temperature range of MgAl₂O₄ transparent ceramics is 1 350 ℃and above, so as a visible/infrared composite optical element, the maximum temperature at which the MgAl₂O₄ transparent ceramics can be reused for a long time is not higher than 1 300 ℃.