A detailed multi-body dynamic model of a heavy truck was established by using SIMPACK software, which included front suspension, rear balance suspension, steering system, tyre system etc. The harmony superposition method was used to simulate stochastic road with a specific spectrum, and an integrated environment with different road roughness was built to study the relationship between vehicle dynamic tyre loads with three directions and different road grading and vehicle speed. Simulation results indicated that, the front axle’s vehicle longitudinal dynamic tyre load was less than the middle and the rear axles, and the front axle’s vehicle side and normal dynamic tyre load was more than the middle and the rear axles. For the middle axle and the rear axle, the vehicle dynamic tyre load was roughly the same. At 60～90km/h driving, on grade A～D road, the front axle’s vehicle normal dynamic tyre load coefficient was more than the middle and the rear axles, and the front axle’s vehicle normal tyre force was less than the middle and the rear axles.