The invention discloses a preparation method of a fixed perforation rock sample. The preparation method comprises the following steps: according to the parameters of fixed perforation on a rock sample, directly obtaining multiple fixed perforation assembly models by a 3D printing machine; fixing the fixed perforation assembly models on the external surface of a steel tube in a well hole; drilling holes in the wall of the well hole along the direction of perforation channels; filling a soluble core material into the perforation channels of the fixed perforation assembly models; after the soluble core material is solidified, disassembling the fixed perforation assembly models; putting the steel tube into a rock sample moulding die, carrying out casting and moulding, performing maintenance under a constant pressure at a constant temperature; and injecting a circulation water detergent into the steel tube to dissolve the soluble core materials in the perforation holes to obtain the rock fixed perforation sample. The included angle between the fixed perforation channels is guaranteed; the included angle between the channels and the axis of the well hole is the same as that of designed scheme so as to satisfy the actual situation of engineering; and the key parameters of perforation channels such as shape, size, distance, and the like can be flexibly set.