Brushless DC fan is widely used in the heat dissipation system of electronic equipment. The fan is usually required to be small in size and have large air volume and integrated speed regulation. A controller is designed for a 12 V brushless DC fan. In order to reduce the cost and volume of the controller, several measures are taken: all electronic components are domestic surface mounted devices, the controller adopts the square wave control algorithm without position sensor, the commutation position of the fan is determined by back electromotive force (EMF) zero-crossing point detection, and three-stage starting is adopted. The prototype fan is manufactured and the experimental platform is built. The starting performance, wind pressure and flow rate of the fan are tested. Experimental results verify the rationality of the controller scheme.