Abstract: On Fluent software platform, Gambit is used to establish the model and grid for the calculation of the counter-rotation axial flow fan. Under constant conditions, the internal flow field of the counter-rotation axial flow fan was simulated; the interface of calculation model in different regions is treated by Interface boundary conditions, and SIMPLE algorithm is coupled with pressure speed to solve Navier- Stokes equation by Segregated implicit algorithm. Combined with the test results of the mode, the aerodynamic performance of the counter-rotation axial flow fan is predicted by the simulation; the internal flow field velocity distribution, the pressure distribution and the turbulence intensity distribution characteristics are obtained, which reveals the internal flow characteristics of rotating fan.