Abstract: The jet cooling technology was introduced and used in the cooling of high power laser mirror, then the water jet cooled mirror was designed. Computational fluid dynamics method was adopted to simulate the jet in a hole by the fluid analysis module FLOTRAN of the finite element analysis software ANSYS, then the influence on the capability of heat transfer of the parameters of the hole was discussed and optimization of the parameters was achieved. The results show that great capability of heat transfer can be achieved by using the jet cooling technology, with simple structure and good controllability, and the heat transfer coefficient can be higher than 100 kW/(m2·K).