In-fracture Multistage plugging is one of the effective means to increase the in-fracture net pressure, activate lateral branch fractures, increase the lateral reconstruction bandwidth, and improve the degree of oil and gas utilization in the reservoir. The investigation of diversion pattern during multistage plugging is of great value for the optimization of multistage temporary plugging in fractures, a numerical model of multistage temporary plugging in fractures was established for the ultra-low permeability fractured reservoir, and the influence rule of approaching angle, stress difference and number of temporary plugging on the opening of branch fractures was studied. The research results show as follows When the horizontal stress difference is beyond 5 MPa, the hydraulic fracture will cross the natural fracture directly at the high approximation angle (≥60°), and it cannot be activated effectively. When the horizontal stress difference is less than 5 MPa and the low approximation Angle (≤ 30°), the hydraulic fracture can open the obtuse branch after encountering the natural fracture. The initial plugging can effectively open the next level of branch joints with high approximation angles, and the secondary plugging can open the secondary branch joints. Using multi-stage temporary plugging in fractures can increase the maximum daily oil production of a single well to two times and the average daily oil production to four times. This work provides the model and method for the design of in-fracture multistage temporary plugging fracturing.