In this study, we analyzed the three dimensional unsteady flow around a motor cooling fan using the vortex panel method. For a popular type of motor cooling fan that has thin blades, we predicted the flow rate through numerical analysis without experimental data, such as the free stream velocity, which is a boundary condition of the flow field. We also calculated the flow rate for various cooling fan geometries and rotating speeds. For these fans, the numerical results showed flow rates within 3% of the experimental results.