Heavy quadruped robots are subjected to uncertain impact loads during foot to ground contact and gait transition, which can easily lead to excessive load on the foot mechanism and structural impact damage. Therefore, a sliding mode impedance control method based on environmental parameter estimation (EPESM) was proposed to solve the problem of poor dynamic performance of using hydraulic series elastic actuators (SEA) as foot ends in unstructured environments. Firstly, based on the piston displacement transfer function of the valve controlled hydraulic cylinder, a SEA impedance control model based on the position inner loop is established, and PID is used as the basic controller; In order to improve the dynamic performance of SEA impedance control, a stable adaptive environment parameter estimation method based on Lyapunov's second method is constructed to compensate for the expected SEA position using feedforward compensation; In order to improve the dynamic performance and adaptability of adaptive environmental parameter estimation methods at different stages of SEA work, fuzzy control methods are used to optimize the adaptive parameters in the adaptive environmental parameter estimation methods; Finally, based on the SEA state equation, a sliding mode controller and a PID controller are constructed for dynamic performance comparison and analysis. The simulation results show that under variable SEA spring stiffness and variable ambient stiffness conditions, the response speed of EPESM impedance control is significantly faster, the adjustment time can be significantly reduced from an average of 5 seconds to within 1 second, the expected displacement and expected contact force can be achieved faster, and the steady-state error can be slightly reduced, keeping the contact force error within ± 6 N. Under dynamic tracking conditions, EPESM impedance control has better dynamic performance, and can maintain a phase delay of within 0.2 seconds and an amplitude error of 5.2 %for a long time after quickly entering the tracking state.