Abstract: To drill long borehole along seam for gas drainage in soft coal seam is always very difficult, and the available drilling techniques can not fully meet the demand of gas efficient drainage, problems of shallow borehole depth and lower hole-making ratio are still existed. Therefore, on the base of medium-pressure compressed air drilling technique, the foam drilling technology used in coal mine is developed , which includes the studies of foam drilling technique, development of generating and grouting system for foam, development of compound drilling technique with medium-pressure compressed air and stable foam, etc. The effect of industrial field tests is very good, the depth of boreholes for gas drainage in soft coal seam can be significantly increased, the discharge of drilling cuttings by foam is efficient, the rotary and drawing pressure of drilling pipe is lower than that of medium-pressure compressed air drilling technique, at the same time, and there is no dust pollution. Because of the above advantages, the foam drilling technique and the compound drilling technique of medium-pressure compressed air and stable foam have wide application prospect in soft coal seam.