This study analyzes the thermal deformation of high-power laser microchannel water-cooling mirrors by coupling the temperature field, obtained through solving the three-dimensional laminar heat transfer equation using the finite volume method, with ANSYS. The performance of microchannel water-cooling mirrors with plate-fin structures and the effects of plate-fin structure parameters on temperature rise and thermal deformation are investigated.Results indicate that under the specified operational conditions, microchannel water-cooling mirrors with parallel plate-fin structures exhibit larger temperature rise and thermal deformation compared to those with traditional parallel inline structures due to the presence of fluid velocity stagnation zones, which reduce the effective heat transfer area. In contrast, microchannel water-cooling mirrors with fork-row plate-fin structures demonstrate significantly lower temperature rise and thermal deformation than those with traditional parallel inline structures. This improvement is attributed to increased convective heat transfer area and enhanced local convective heat transfer efficiency. Additionally, the heat transfer efficiency of the fork-row plate-fin structure increases with the Reynolds number. This study proposes a new structure for reducing the thermal deformation of high-power laser mirrors.