The tracked vehicle has good passability and adaptability for different complex environments, and also can maintain a stable posture with the ability to regulate flexible posture. Therefore, it is necessary to design a steering system with continuous and accurate steering radius and high transmission efficiency. The dynamic model of differential steering system was established including input rotate speed and output rotate speed. The dynamic model between input rotate speed and steering radius was obtained according to the relationship of output rotate speed and steering radius. The dynamic model of steady steering including the length, gauge, ground instantaneous center offset and so on of tracked vehicle was built, which could be used to predict the steady state steering characteristic of tracked vehicle.