ZnSe is an important semiconductor material of II-VI group. It exhibits a zinc blende (ZB) structure at room temperature and pressure, and the phase transition into a rock salt (RS) structure occurs under high pressure. Doping transition metal ions (TM ²⁺) into the ZnSe crystal can effectively produce laser gain media and photoelectric materials in the mid-infrared region, which exhibit important research significance. This study mainly deals with the effect of high pressure on the properties of the Cr ²⁺-doped ZnSe semiconductors. Further, the effect of dopant (Cr ²⁺) on the phase transition pressure of ZnSe and the changes of electronic structures, optical properties, and mechanical properties of ZnSe and Cr ²⁺∶ZnSe are calculated under high pressure using the first-principles calculations based on the density functional theory. The introduction of the dopant (Cr ²⁺) reduces the phase transition pressure of ZnSe from ZB structure to RS structure, and this trend continues with a further increase in the doping concentration. The electronic structures and optical properties of ZnSe and Cr ²⁺∶ZnSe are evaluated under high pressure, and ZnSe is found to shift from exhibiting semiconductor properties to exhibiting metal properties under high pressure. The calculated elastic constants of the crystals satisfy the stability conditions under both ambient and high pressure. Meanwhile, the large bulk modulus, shear modulus, and Young's modulus of the crystal under high pressure indicate that the RS structure exhibits considerable hardness and stability and is remarkably resistant to deformation under external influences.