Abstract: In order to study hydraulic fracture extension rule in coal reservoirs, microseismic data of 15 hydraulically fractured wells had been chosen in Zhengzhua ng block, Qinshui Basin. Based on the data of fracture direction, length and height, the geological controlling factors of fracture extension were integratedly investigated from four aspects:coal petrology characteristics, rock-mechanics property, crustal stress conditions and the pre-fractures. The results showed that the hydraulic fracture s orientation were nearly NEE, along the direction of the maximum horizontal principal stress. The vertical fractures were well developed in the study area. The hydrauli C fractures extended more easily in the relative high coal rank reservoirs. Moreover, the fracture length depended on the coal maceral compositions, and they decrease d with increasing tension strength and elastic modulus. Meanwhile, the rock-mechanics property difference between the coal seam and its roof /floor could effectively li mit the extension of vertical fractures. The closure stress increased with the coal seam depth, but because of the pre-fractures, there was a low correlation between the fracture length and burial depth.