A computational fluid dynamics (CFD) method for semiconductor laser external heat dissipation numerical simulation is introduced. For fluid-solid coupled heat transfer problems, convection-conduction coupled heat transfer model and mass conservation, energy conservation, momentum conversation, k-ε equation governing equations are established; precise numerical solution can be acquired by iterative calculation according to specified boundary conditions. The forced air cooling design for a semiconductor laser (15 W maximum heat load) with external heat dissipation, which consists of an aluminum alloy heat sink and an axial fan, is simulated with CFD method; the result of numerical simulation indicates that the design is applicable for the thermal requirements of the system.