Abstract: In the development process of tight sandstone reservoir by horizontal well refracturing, the effective increase of the postfrac stimulated reservoir volume (SRV) is the key to success. Due to the limitation of initial fracturing completion process, the distribution of hydraulic fractures and natural fractures in the reservoir, and the dynamic change of pore pressure field and stress field caused by reservoir production and oil drainage after fracturing, however, different fracture clusters of horizontal well refracturing can hardly propagate evenly to achieve satisfactory stimulation effect. With Yuan 284 Block of tight sandstone reservoir in the Changqing Oilfield as an example, the optimization procedure of horizontal well refracturing process was established by using the finite element method-discrete fracture network (FEM-DFN) method and the four dimensional dynamic stress field cross-coupling method. After the full three dimensional volumetric fracturing numerical model considering the distribution of natural fractures and the dynamic change of in-situ stress was established, the optimization of horizontal well refracturing was studied. The multi-fracture even propagation laws of horizontal well refracturing in tight sandstone reservoirs were revealed, and the technological parameters of horizontal well refracturing were optimized, so as to reach the goal of increasing SRV of tight sandstone oil reservoir by horizontal well refracturing. It is indicated that FEM-DFN method can accurately and reliably describe the geometry of fractures induced by horizontal well refracturing. The fracture network complexity degree and lateral propagation degree after horizontal well refracturing can be improved by optimizing the technological parameters of horizontal well refracturing, including timing, sand amount in fractures, cluster spacing, injected fluid volume and construction displacement. Furthermore, the field implementation case indicates that the field implementation based on the horizontal well refracturing process considering the dynamic change of four dimensional in-situ stress presents remarkable effects, which is of important guiding significance for the process optimization of horizontal well refractuirng in tight sandstone oil reservoirs at home. The research provides a reference for the optimization of horizontal well refracturing process and a theoretical basis for the improvement of tight sandstone reservoir development.