The invention discloses a method for acquiring the opening time of a natural fracture under the condition of in-fracture temporary blocking. The method comprises the following steps that stratum physical property parameters are obtained according to field geological data; a hydraulic fracture is divided into N units equal in length, the N units are numbered in sequence, and the length of each unitis L/N; meanwhile, the moment of in-fracture temporary blocking is adopted as the initial moment t0, the total calculation time t is divided into m time nodes at equal intervals, and the interval time of the adjacent time nodes is t/m; the width of each unit in the hydraulic fracture at the initial moment is calculated; the pressure of fluid in the hydraulic fracture at the kth time node is calculated; closing stress borne by the positions, on the upper side and the lower side of the hydraulic fracture, of an inlet of the natural fracture at the kth time node is calculated; and whether the natural fracture is opened or not is judged according to the judging criteria. According to the method, the principle is reliable, the calculation precision is high, the opening time of the natural facture in the process of converting in-fracture temporary blocking to pressure fracturing can be precisely calculated out, and then effective guide is provided for pressure fracturing scheme design.