Due to the wide working range of the proportional servo valve (PSV), the flow force changes greatly with the load pressure drop, which significantly affects the precise control of the valve spool position of the PSV. An adaptive sliding mode control based on the immersion and invariance principle (ASMCII) is designed in this paper to solve this problem. The load pressure drop is adaptive to the pressure senseless PSV, and then the ASMCII is used to achieve high precision control. Firstly, the dynamic model of PSV system under unknown large flow force disturbances is established, and the sliding mode control strategy based on reaching law is designed and applied. Secondly, in the design of disturbance estimation error manifold, the immersion and invariance principle (I&I) are applied to ensure the estimation error of load pressure drop converges to 0, for the sake of the accurate estimation of flow force. Finally, the stability analysis and simulation of the system are carried out. The results show that under the simulation conditions of 0–35 MPa, ASMCII converges uncertain pressure drops quickly to compensate flow force completely, which promotes both static and dynamical performance significantly contrast to PID and the sliding mode control.

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