ZnSe semiconductor material is an important raw material for preparing optoelectronic devices and photocatalytic reaction catalysts. The monomer material exhibits deterioration under strong light and electron-hole recombination. In this study, ZnSematerials were prepared by element doping, and the optical and structural properties of ZnSe enhanced by element doping were studied and compared with those of monomer materials. Pure ZnSe and Mn/Zn with doping ratios of 5%, 10%, 15%, and 20% were prepared by the hydrothermal method in the laboratory to compare the morphology, structure, light absorption, and catalytic performance of the composite materials. The results showed that the sample with a doping ratio of 10% had the highest crystallinity, the least impurities, and the best catalytic performance. Subsequently, the high-pressure structural phase transformation behavior of pure ZnSe and samples doped with 10% Mn/Zn was investigated by in-situ Raman spectroscopy using Diamond Anvil Cell to explore the effect of element doping on the structural properties of the samples. The results are as follows: (1) Scanning electron microscope (SEM) images show that the morphology of the ZnSe sample prepared with Mn element is spherical and similar to the pure sample. Small particles are on the surface of the spherical particles, and with the increase of Mn addition, more substances are loaded on the surface. (2) X-ray diffraction (XRD) patterns show that the structure of the ZnSe sample is a cubic zinc blende structure. With the increase of Mn addition, the characteristic peak of MnSe in the sample is enhanced and the formation of impurity MnO2 is more completed. The sample with a doping ratio of 10% has a high ZnSe crystallinity and a low impurities formation. (3) Solid-state ultraviolet diffuse reflectance (UV-Vis) results show that the sample with a doping ratio of 10% has the maximum light absorption edge and the smallest bandgap width of 1.65 eV. (4) The results of the photocatalytic experiment show that the sample with a doping ratio of 10% has the highest efficiency in catalyzing the degradation of methyl orange, with a degradation rate of 85.4% in 6 hours. The study demonstrates that the ZnSe composite material doped with 10% Mn element has the best relative optical absorption and catalytic performance. The high-pressure phase transition of ZnSe samples and samples with a doping ratio of 10% were investigated using Diamond Anvil Cells combined with in-situ Raman spectroscopy. The results show that: (1) The LO phonon mode of pure ZnSe disappears at a pressure of 12.3 GPa, and the TO phonon mode disappears at a pressure of 20.8 GPa. No new peaks are generated during the entire pressure process, indicating a high-pressure behavior of the pure ZnSe phase transition from the zincblende phase to the rocksalt phase. (2) The TO phonon mode of the composite material splits at 6.9 GPa, and a new peak appears at 208 cm-1 at 8.0 GPa, indicating that some samples transform from the zincblende phase to the wurtzite phase at this pressure. The peak of the wurtzite phase disappears at 10.8 GPa, and the system undergoes a phase transition from the wurtzite phase to the rocksalt phase. When the pressure is increased to 18.8 GPa, the LO phonon mode is very weak and almost disappears, indicating that the zincblende phase in the system has completely transformed into the rocksalt phase. This study investigated the photo-catalytic performance and phase transition behavior of ZnSe under different conditions and explored the effects of different doping ratios on the photo-catalytic performance of ZnSe, determining that the sample with a doping ratio of 10% is the best composite material, which enriches the diversity of the physical and chemical properties of ZnSe under extreme conditions.