Abstract: The complicate stress distribution around horizontal well-bore makes hydraulic fracture reorientation happen, but the principles behind the reorientation are poorly understood. A three-dimensional reorientation model for hydraulic fractures around horizontal well-bores is established, based on the maximum tensile stress criterion and the Lagrange Multiplier method. The model can be used to analyze initiation position and propagation shapes of hydraulic fracture, with three geo-stresses and well-bore pressure being considered. Numerical codes are made for simulation. Based on theoretical model, laboraroty experiments with rock samples are performed on the true tri-axis simulation equipment for hydraulic fracturing. The numerical results from the theoretical model are basically consistent with those of experiments. The results indicate that the three-dimensional reorientation of hydraulic fractures around horizontal well-boles exists, and the distance away from a well-bore after reorientation increases when the well-bore orientation becomes larger, and generally occurs within three times the size of well-bore diameter.