In this work, the design and analysis of a hydropneumatic slow active suspension with leveling system is developed. The design based on a hydropneumatic suspension unit with a shock absorber element of an existing car and an electrohydraulic servo valve. A nonlinear mathematical model of a quarter car with active suspension system is deduced. The mathematical model considers the real dynamic behavior of the hydropneumatic suspension unit and the electrohydraulic servo valve. The classical control theory is used to design the control system of the active suspension system, a proportional derivative controller (PD) is used for leveling system control and the proportional integral controller (PI) is used for controlling and minimizing the vertical body acceleration due to the road irregularities. Using the MATLAB tool kit, a simulation program for the designed system is developed. The main suspension disturbances, road irregularities, and the inertial forces are modeled and simulated. The tire is simulated by linear damper and linear spring. The simulation model is used to predict the dynamic response of vehicle body under different types of roads and dynamic loads. The simulation model is also used to compare the performance of the designed active system with the passive system.