With the development of shale gas, infilling the existing horizontal well pattern will be the key to later development. Continuous exploitation of old wells will cause redistribution of pore pressure and in-situ stress. The redistribution of in-situ stress has a significant impact on the fracture propagation behavior and path. In order to explore the influence mechanism of in-situ stress redistribution on fracture propagation behavior, based on the block discrete element numerical simulation method, the influence characteristics of the change of in-situ stress field on the hydraulic fracture propagation of infill wells are studied. In this study, the effects of injection rate, fracturing fluid viscosity, in-situ stress gradient and initial in-situ stress on hydraulic fracture propagation are considered. The results show that the decrease of in-situ stress caused by old wells will lead to the migration of hydraulic fractures from new wells to old wells. Increasing injection rate and fracturing fluid viscosity can reduce hydraulic fracture migration caused by non-uniform in-situ stress. The larger the in-situ stress gradient and the higher the initial in-situ stress field, the higher the hydraulic fracture migration rate. This study has a certain theoretical significance for the formulation of shale gas horizontal well infill program.