The test method of vehicle stability under extreme adhesion conditions based on the unsteady constraint test system was proposed. The unsteady constraint test system model was set up. Based on the Matlab/Simulink, the dynamic simulation system of unsteady constraint dynamics test system for the Chery A3 car was established. Using the simulation model, the stability control performances of the independent vehicle with or without ESP and test system under extreme adhesion conditions was simulated and analyzed. The study results indicate that the test method of vehicle stability under extreme adhesion conditions based on the unsteady constraint test system is feasible, safe and reliable, which could provide a reliable test platform and effective test verification method for researching and designing ESP control system.