Based on the heat-fluid-solid multiphysics coupling method, the fluid flow, convective diffusion and thermal conduction, which occur in the pumping and cooling processes of high power disk-type laser, are simulated and analyzed. Influences of pumping power and fluid flowing velocity on the temperature distribution of disk gain medium are studied. Simulation results reveal that the temperature of cooling fluid gradually increases in the fluid flowing direction under the interaction of flowing, heat conduction and convective diffusion. Temperature distribution of the laser gain medium is asymmetrical in the direction of fluid flowing direction. The highest temperature position on the flowing direction is shifted from the axis of gain medium. A linear variation of temperature differences on the flowing direction of gain medium between the inlet and outlet is showed with the pump power increasing. A nonlinear variation of temperature difference on the flowing direction of gain medium between the inlet and outlet is showed with the fluid flowing velocity increaseing. Experimental results are in agreement with the simulation results.