In the coal bunker of coal washing plant, raw coal storage would form a comfined space with coal bunker. It was easy to accumulate gas in this space because of raw coal gas diffusion.  Fans were usually used by coal enterprises to carry out gas drainage. Principles of frequency converter and its current situation at home and abroad were introduced in this paper, a technical scheme was proposed to control fan speed with frequency conversion, which not only realized  automatic control of fan operation and accurate adjustment of fan speed, but reduced energy consumption and solved problems of traditional fans adopting a baffle plate and the valve to control the air flow. The results showed that this technique had strong potential for promotion in coal mine.