There are lots of factors that affect the dynamic load induced by high-speed train; the train speed is one of the most critical factors. It is rather difficult to determine the effect of train speed on dynamic load using theoretical method due to the complexity of vehicle-track-subgrade interaction. Large-scale physical model test has gradually become one of the most popular approaches for studying the dynamic characteristics of ballastless track structure of high-speed railway. A full-scale model of ballastless track subgrade was constructed based on the design and construction standard for high-speed railway line from Shanghai to Nanjing. The dynamic strain of type I slab and dynamic soil pressure of subgrade were obtained by conducting single wheel axel exciting test. The relationship between dynamic load and train speed was presented. The dynamic load magnification factors of slab and subgrade structure under different train speeds are obtained respectively. The magnification factors are of great significance for designing the dynamic load in type I track-subgrade system.