To address issues such as auto-focusing system fault analysis and component selection, and to improve the focusing accuracy of aerial remote cameras, this article offered insights into the auto-collimated focusing technology based on the Ronchi grating.First, in this paper,several common focusing methods of both domestic and foreign aerial cameras were summarized and compared. Then, the composition and operating principle of optoelectronic auto-collimated focusing systems based on the Ronchi grating were introduced, the mathematical model was established, and the simulation curves of the focusing waveform with different imaging positions were presented. To measure the focal distances, the concept of the defocusing evaluation factor was proposed.Next, the three factors that affect the focusing accuracy of the diffraction effect and the aberration of the optical system, the period selection of the Ronchi grating, and the energy distribution of the light source were analyzed. The influence of the Ronchi grating period selection method was then presented. Finally, the experimental results verify the validity of the simulation results and show that the peak-to-peak ratio of the focusing waveform is 0.82, corresponding to an average focusing detection resolution of 10% at 0.05 mm.