Abstract: In the hydraulic unit, the seal between the rotating shaft unit and rotating sleeve unit generally is realized by rectangular sealing ring, and the seal effect directly affects the working status of the rotating shaft, so rectangular sealing ring plays an important role in the hydraulic unit. Based on the actual situation, firstly 3D-model of rotating unit was built with SolidWorks software, and then the model was predigested reasonably according to the analysis object and content. The stress cloud of the rectangular sealing ring was simulated by ANSYA software under three pressure conditions, and the dangerous zone was gained. This study can provide reference and basis for the optimized design and safe use of rectangular sealing rings.