Abstract: The unsteady and energy conversion characteristic of vehicle during cornering and braking condition were analyzed based on generalized energy law and energy phase plane method.A 9DOF vehicle nonlinear dynamic model considering the load transfer characteristic to evaluate the energy transfer combined with the ‘Magic formula’ tire model was proposed, its reliability was validated using the stability measurement system based on inertial measurement principle and VBOX device. The vehicle stability and the energy conversion model weredevelopedby using generalized energy law and energy phase plane method, and the time-varying and transform characteristics of the vehicle system energy was analyzed at cornering-braking condition under MATLAB simulation environment. The results point out thatthe initial braking time zone is thekey section to vehicles' unsteadiness and control, the yaw control is the main factor when the steering angle is small and the yaw-lateral control should be taken into account as well when the steering angle is large. The study offers critical theory of parameter selection of segmentation control for vehicle stability.