A new type of photonic crystal mirror was proposed as the P-side mirror of the vertical-cavity surface-emitting laser, and the reflection characteristics of the photonic crystal mirror were studied and analyzed by using the three-dimensional finite-difference time domain method. In this paper, taking 850 nm vertical-cavity surface-emitting laser as an example, a photonic crystal mirror suitable for it was designed. To make photonic crystal mirrors meet the requirements of 850 nm vertical-cavity surface-emitting lasers for mirrors, it needs to have high reflectivity and wide bandwidth in the 850 nm band. The structural parameters that need to be optimized in the photonic crystal mirror include a grating layer, a two-dimensional photonic crystal layer, and a spacer layer between the grating layer and the two-dimensional photonic crystal layer. It can be seen that many structural parameters need to be optimized, so the control variable method is used to optimize the parameters. Because our research group has done a lot of research on grating structure, to reduce the amount of calculation, it is necessary to optimize the two-dimensional photonic crystal structure first and then optimize the grating structure. After optimization calculations, the optimal structural parameters of the photonic crystal mirror are that the grating period is 636 nm, the thickness is 162 nm, the duty cycle is 16.35%, the thickness of the spacer layer is 86 nm, and the air hole radius of the two-dimensional photonic crystal structure is 84 nm, the period is 212 nm, and the height is 90 nm. When the photonic crystal mirror has optimal structural parameters, its high reflectivity bandwidth in TE optical mode is 106 nm, and the ratio to the central wavelength is 12.5%. At this time, the reflectivity of the photonic crystal mirror at the center wavelength of 850 nm is greater than 99.5%. However, the reflectivity in the TM optical mode is lower than 80%, so the photonic crystal mirror not only meets the requirements of the vertical-cavity surface-emitting laser for the mirror, but also has a wide polarization selectivity. In terms of the thickness of the mirror, the overall thickness of the photonic crystal mirror is very thin. Its thickness is 338 nm, which is 12.4% of the thickness of conventional P-type distributed Bragg mirrors and 61.7% of the thickness of high-contrast subwavelength grating mirrors. In terms of thermal conductivity of materials, the equivalent thermal conductivity of the photonic crystal mirror is 46% higher than that of the distributed Bragg mirror, so the photonic crystal mirror has good equivalent thermal conductivity. Therefore, considering factors such as the thickness of the mirror and the equivalent thermal conductivity, the photonic crystal mirror is beneficial to heat dissipation and improves the optoelectronic performance of the laser. In addition, the etching depth of the photonic crystal structure of the photonic crystal mirror is relatively small, so it will hardly affect the series resistance and current density. Moreover, the two-dimensional photonic crystal structure has strong optical confinement, which is also beneficial to further reduce the threshold current density of the laser. In addition, the photonic crystal mirror also avoids the stress problem caused by volume shrinkage after oxidation of high-aluminum compounds in high-contrast subwavelength gratings to form low-refractive-index oxides.Therefore, the new photonic crystal mirror proposed in this paper can replace the P-type distributed Bragg mirror of the traditional vertical-cavity surface-emitting laser. At the same time, photonic crystal mirrors are conducive to promoting the rapid development of vertical-cavity surface-emitting lasers in optical communication, optical interconnection, and optical information processing.They also conducive to promoting vertical-cavity surface-emitting lasers to enter new application fields continuously.