Abstract: Through analyzing blasting similar rate, dynamic similarity conditions and failure mechanism of engineering rock at a tunnel exit, the paper describes the similar parameters and dynamic similarity problems of blasting model test. Focusing on the similarity relation of the thrown distance of on-site blasting model test, based on projectile accumulation method, it concludes that the approximate ratio of thrown distance and geometric similarity is 4/3 power. It meets the project needs that thrown distance can be directly designed by geometric similarity in a large-scale on-site blasting model test.