Abstract: The steering performance of tracked combine harvester working in paddy field is quite different from steering on hard ground because of the sticky and high moisture of the soil. The unmodified kinematic model of tracked combine harvester can not be used to design the automatic navigation controller of tracked combine harvester working in paddy field. A kinematics model of tracked combine harvester working in paddy field was established in this study. Based on the kinematics model, the relationship between the slip rate, skid rate, steering radius, steering angular velocity, and track winding speed was deduced. The steering radius correction coefficient and steering angular velocity correction coefficient were proposed to describe the relationship between the actual steering parameters and theoretical parameters. The effects of soil physical characteristics on track slip was analysed. In order to study the tracked combine harvester steering kinematic parameter in paddy field, a testing system was built. The winding speed of the tracks were obtained by monitoring the speed of the driving wheels on both sides of the track. Limiting average filter was used to process speed signal. The variance of speed signal decreased by 60.8% when filter window width was 10 sampled data. Extend Kalman Filter (EKF) was used to merge GPS and IMU date to obtain the trajectory and course of combine harvester. The standard deviation of course decreased by 53.6% compared with the data GPS only. Eleven groups of field experiments were carried out at different forward speeds. The forward speed range was 0.408-1.466 m/s which covering the working speed range of tracked combine harvester. Field experiment showed that the vehicle forward speed was slightly less than the track winding speed, the slip rate of low speed track increase with the increase of steering speed and close to 1, and it was in complete slip state. Skid rate increased with the increase of forward speed in the range of 0.066-0.378. Under the influence of steering slip and skid, the actual steering radius increased with the increase of steering speed. The actual steering angular velocity increased with the increase of steering speed, which had a same variation trend with the theoretical value, but the change rate was less than that of the theoretical value. The increasing of shearing on soil enlarged the skid rate and slip rate of track, leading to the lateral offset of steering pole. The actual steering radius and actual steering angular velocity were related to slip rate, skid rate and forward speed. The range of the steering radius correction coefficient was 1.737-2.947, which was a quadratic function of the forward velocity. The variation range of the correction coefficient of steering angular velocity was 0.315-0.677, which was a power function of the forward velocity. The steering kinematics model could be modified by the steering radius and steering angular velocity correction coefficient, which can provide theoretical basis and reference for tracked combine harvester navigation controller.