The invention provides a making method of an internal precrack of a rock specimen. The making method comprises the following steps of a step I, cutting the rock specimen; a step II, making of a crack: processing a precrack by using a machine tool or a water jet cutter, carrying out perforation on two end surfaces of a specimen unit, namely the cut surfaces of the rock specimen, so as to further form the crack; a step III, splicing the specimen units; a step IV, maintenance of a spliced specimen: after the splicing is completed, adopting normal-pressure evaporation maintenance, after the maintenance is finished, standing and air-drying the spliced specimen in a natural condition, and then removing high-strength cement protruding from the surface of the spliced specimen by using fine sandpaper or a wet duster. The method is low in manufacturing cost, is convenient in making, and can be used for carrying out batch making.