Abstract Distributed drive electric vehicle (EV) is driven by four independent hub motors mounted directly in wheels and retains traditional hydraulic brake system. So it can quickly produce driving/braking motor torque and large stable hydraulic braking force. In this paper a new control allocation strategy for distributed drive electric vehicle is proposed to improve vehicle's lateral stability performance. It exploits the quick response of motor torque and controllable hydraulic pressure of the hydraulic brake system. The allocation strategy consists of two sections. The first section uses an optimal allocation controller to calculate the total longitudinal force of each wheel. In the controller, a dynamic efficiency matrix is designed via local linearization to improve lateral stability control performance, as it considers the influence of tire coupling characteristics over yaw moment control in extreme situations. The second part adopts a longitudinal force allocator to separate each longitudinal force into motor torque and hydraulic pressure based on actuators' output characteristics. A Carsim and Matlab joint simulation is carried out under the double lane change condition and the simulation results demonstrate that the proposed control strategy achieves a better performance in lateral stability control than that without hydraulic system. It can be concluded that the strategy is able to broaden the working range of in-wheel motor in vehicle stability control. Introduction The energy-saving and stability have always been the main theme of electric vehicle's development. Distributed drive electric vehicle has an excellent prospect in the study of vehicle stability control due to its new driving form and precisely controllable driving/braking torque [1]. To take advantages of quick response and precise control character of in-wheel motors, a series of allocation research has been done. Masato Abe and Ono designed different optimal objectives for longitudinal force allocations [ 2]. Zou Guangcai [ 3] put forward tire longitudinal force optimization distribution method to improve direct yaw moment control (DYC) performance. But for in-wheel motor, the capability of torque output is limited, so the yaw moment generated only by motors is not enough to keep vehicle's stability especially in extreme situations. Consequently, the hydraulic system is coordinated to improve the control performance when motor reaches its limit. Yimin Gao [ 4] proposed three distribution strategies of braking force and finished the regenerative braking simulation under urban conditions; Konghyeon Kim [5] distributed total braking force into motor force and hydraulic force by fuzzy control, aiming to improve energy recovery efficiency; Okano and Castro [ 6-7] used frequency separation methods to separate the electric braking force and hydraulic braking force in hybrid ABS. However, early studies about coordination control of motor and hydraulic system mainly focus on the longitudinal dynamics control and brake energy recovery. They do not apply for the lateral dynamics control and could not solve the problem of actuator limit in yaw stability performance of the vehicle. In this paper a control allocation strategy is introduced to improve lateral stability based on in-wheel motors and hydraulic brake system of distributed drive EV . The simulation performed on Carsim/ Simulink platform is carried out to verify the validity of the strategy. Stability Control System Based on In-Wheel Motors and Hydraulic Brake System The stability control system of distributed drive EV is shown in Figure 1. Four hub motors are equipped in each wheel respectively and traditional hydraulic system is retained. Each motor controller receives allocation results from stability controller and imposes force on wheel. While hydraulic pressure of each wheel can be controlled by HCU which also gets hydraulic signals from the controller. Previ