In the process of position output control of closed pump-controlled servo system, there will be some problems such as difficulty in modeling asymmetric cylinder, uncertainty of parameters and difficulty in debugging control algorithm. Therefore, an adaptive backstepping control strategy ( controller ) was proposed and its feasibility was verified by hardware-in-the-loop simulation platform. Firstly, the mathematical model of the direct-drive pump-controlled asymmetric cylinder hydraulic system considering the check valve and the relief valve was derived, and the state space equation of the system was re-written. Secondly, by introducing the form of vector, the mathematical model was re-written into a strict feedback form, so as to design a new adaptive backstepping controller to solve the problem of simulation parameter uncertainty to realize the accurate control. Finally, under the Linux + Preempt-RT semi-physical simulation platform, the step signal, sinusoidal signal and sinusoidal signal test with time-varying load of the adaptive backstepping control of the direct-drive pump-controlled asymmetric cylinder position system was completed, the adaptive backstepping control result was compared with the traditional PID control result. The research results show that the steady-state accuracy of the adaptive backstepping control method can reach ± 3. 98 mm, which is 53. 6 % higher than the traditional PID control accuracy. At the same time, the parameter adaptive law adjusts and estimates the system uncertainty parameters in real time during the system position control process, which can present a good adaptive dynamic approximation process. In summary, the results verify the good tracking performance and robustness of the proposed control strategy. [ABSTRACT FROM AUTHOR]