This paper, based on a case study on No.4 coal seam of Dafosi well field, Binchang district, analyzes its reservoir physical properties, water sensibility, surface water quality and compatibility, anti\|swelling agent's features and harmfulness, and selects appropriate active hydraulic fracturing liquid system, aiming at providing references for Binchang district or similar regions to develop ground CBM. Results show that the No.4 coal seam bears less quantity of expansive clay minerals, and coal permeability is positive to fracturing water mineralization, with a strong water sensibility. Optimization of fracturing liquid formula indicates a good compatibility of ground water and coal reservoir water, good to be used as fracturing water. 1.5% KCl solution, less harmful to reservoir and less costly, may be used as anti-swelling agent. This final fracturing liquid formula is written as ground water+1.5% KCl anti-swelling agent + 0.3% DB-80 cleanup additive.