Abstract: In order to study the influence of different positions, angles and sizes of cracks in the coal and rock on the grouting-induced cracking, the physical similarity simulation test method is adopted, and different prefabricated cracks are set in similar samples of the coal and rock for grouting test. Similar sample cross section, acoustic emission monitoring result and pump pressure curve, the crack propagation law of similar sample with prefabricated cracks is studied. The research shows that: when the prefabricated cracks do not intersect with the grouting hole, the development process of grouting fracturing fissures for similar samples of coal and rock with prefabricated fissures includes four stages: splitting through, grout filling, fissure splitting, and splitting expansion; as the size of the prefabricated fissure increases, the split fissures are more likely to develop in the direction of the prefabricated fissure; after being penetrated with the prefabricated fissure, the newly developed split fissures tend to expand outward along the angle of the prefabricated fissure; when they intersect, there is no splitting. The rupture stage, angle and size of the prefabricated fissures even determine the development direction of the split fissures.