Abstract: Critical surface tension is a significant parameter to reflect the wetting property of solid surface. It prepares the JFC solutions at different concentration (different surface tension) by using the specimens of coal sample which are compacted by self-designed shaping mould. The critical surface tension of four coal samples is obtained from coal-water contact angle test by FTA200 surface tension analyzer and contact angle analyzer. The results show that the critical surface tension of coal ranges from 20.94 to 28.59 mN·m^-1,coal belongs to low-energy solid surface; In the process of water injection for the practical coal, the surface tension of the common water in coal mines is greater than coal's, which leads to poor wetting effect of coal; When the surfactant is put into the injection water, the surface tension of water can decrease to less than coal's critical surface tension, and the coal can be full wetting, which gets good dust suppression effect.