Abstract: Hydraulic fracturing technology has been used more and more in the roadway with strong dynamic pressure for pressure relief in recent years. The key issue of hydraulic fracturing is how to control the crack orientation,expansion direction and path of hydraulic fracture. The length of the connection between the crack starting point and the point with a 1 / 2 slot angle on the crack spreading path is defined as the crack deflection distance and as the key test indicators. The effects of different pump flow on the deflection distance of fracture during hydraulic fracturing of 300 mm×300 mm×300 mm reserved drilling and longitudinal grooves cement block are studied using a large size true triaxial test. The results show that the vertical slit hydraulic fracturing crack is first cracked along the chipped direction and gradually turns to the maximum main stress during the process of expansion. The cracks are in S-type asymmetric form and relatively single and there are no complex micro-cracks. The cracks expand along the longitudinal while expanding horizontally and there is no large deflection during the expansion process. Three stages are characterized during fracturing process:the initial fracturing stage,the continuous ex-pansion stage and the fracture penetration stage.With the increase of pump flow,the fracturing pressure is slightly increased and the fracturing time is significantly shortened. At the horizontal stress ratio of 1.5,the pump flow increases from0.5mL / s to 1.0mL / s,the crack deflection distance increases by 54.9% . Pump flow increases from 1.0 mL / s to 1.5 mL / s,the crack deflection distance increases by 16.7% . With the increase of pump flow,the deflection distance of cracks increases obviously,and the increasing trend is semi-parabola. Under the horizontal stress ratio of 2. 0,the pump flow increases from 1.0mL / s to 1.5 mL / s,the crack deflection distance increases by 30.6% . The pump flow increases from 1.5 mL / s to 5.0mL / s,the crack deflection distance increases by 67. 9% . Compared with the stress ratio of 1.5,the deflection distance of crack decreases obviously under the same pump flow condition. The real triaxial test method can only be used to test the physical model of the small size test block. A suitable numerical calculation method will be selected to further carry out the experimental study on the hydraulic fracturing effect of large-scale rock formations.