Objective Aiming at the problem of precise tracking control of trailer to target trajectory for a tractor-trailer wheeled mobile robot with an on-axle hitching a double-loop control method was proposed which can track the relative curvature of ideal trajectory curve of the trailer. Methods Firstly the kinematics model of tractor-trailer wheeled mobile robot with an on-axle hitching was established by combing the nonholonomic constraints and its dynamics model was established by Euler-Lagrange equation. Then an important function relation between the relative curvature of the ideal trajectory curve of the trailer and the difference between the ideal yaw angle of the tractor and the trailer was derived by using the kinematic equation. Finally based on the core relation a double-loop control method consisting of the outerloop speed controller of the attitude error system and the inner-loop proportional-integral feedback controller of the dynamic model was used to realize the given tracking task. Results The simulation results showed that for the outer-loop system,the outer-loop speed controller made the attitude tracking error all approach to zero after a period of change and the actual attitude variable finally approached to the target attitude variable stably. For the inner-loop system the inner-loop proportional-integral feedback controller made the speed tracking error approach to zero after a short adjustment and the actual speed value finally approached to the reference speed value stably. Conclusion The designed double-loop controller can effectively realize attitude tracking and speed tracking and make the trailer accurately track the ideal trajectory curve. Because the relative curvature of the trailer trajectory curve is introduced in the attitude tracking process this method can greatly improve the accuracy of trajectory tracking