In considering the magnetic flux distribution of the permanent magnet near the rotor, a dynamic model of an open-loop voltage single-phase BLDC cooling fan motor has presented in this paper. Basing on the dynamic model, the commuted angle is optimized. The optimal angle of commutation is verified by a single-phase BLDC cooling fan. In addition, the test result shows that the peak current during the phase changing has reduced apparently, and the efficiency has improved by around 8% in average comparing with the lag angle commutation and the lead angle commutation.