Jet cooling technology is used in mirror cooling of high power lasers and water jet cooled mirror is designed based on this. 2D model is built and validated to calculate the convective heat transfer coefficient and pressure of liquid under certain parameters by fluid analysis module FLOTRAN in finite element analysis software ANSYS. 3D model is built to calculate corresponding temperature and deformation distribution of the mirror by the module of multi-physics in ANSYS, and the performance comparisons of different materials and different cooling methods are made. The results show that water jet cooled SiC mirror exhibits small mirror deformation, simple structure，good cooling uniformity and good pressure characteristic, which has great prospects in the application of high power lasers.