PurposeInternal leakage is one of the key factors that influence the super-low speed performance of continuous rotary electro-hydraulic servo motor. Therefore, this paper aims to study the change rule of internal leakage for improving the low speed performance of motor.Design/methodology/approachThe mathematical models of internal leakage of continuous rotary electro-hydraulic servo motor were established, and according to the working principle of the motor, the 3D models of internal leakage location were established. Simulation analysis was implemented on the continuous rotary electro-hydraulic servo motor by the finite element analysis software ANSYS based on the fluid-structure interaction theory.FindingsThe results show the deformation of motor’s key parts and the changing rule of internal leakage. The effect of the leakage to the low speed performance of electro-hydraulic servo motor was analyzed, and at the same time, the motor’s leakage experiment was also conducted to verify the validity of simulation results.Originality/valueThis paper lays the foundation for improving the low speed performance of motor.