Abstract: The influences of rock joints on the formation of blasting fragmentation have always been a hot issue in blasting engineering, which is one of the most important factors affecting the construction efficiency and long-term operation safety. Based on the explosion tests on the graded materials of Yulongkashi Water Conservancy Project, the influences of rock joints on the formation of blasting fragmentation are studied. The test results show that the fragmentation with rock particle size below 5 mm is mainly formed by the blasting loads and dynamic compressive strength but rarely by the rock joints. However, the influences of the rock joints on the fragmentation rock particle size above 5 mm are significant, which is reflected in the partition characteristics for the formation of rock blasting fragmentation. Further, the numerical simulation of rock blasting fragmentation is carried out by using the LS-DYNA secondary development technology, and the mechanical mechanism of the rock joints on rock blasting fragmentation is analyzed. The results show that the rock joints greatly affect the stress wave propagation in the fracture zone but produce a small effect on the formation of the fragmentation wiht small rock particle size, which is verified by the test results. Based on the dual influences of rock blasting fragmentation and rock joints, a partition prediction model for the rock blasting fragmentation is proposed. The rock blast fragmentation for many test samples is predicted by the proposed model and the existing models. By comparing the predicted results, it is found that the proposed model has a higher accuracy in predicting rock blasting fragmentation.