The state observer method is applied in the vehicle safety and stability systems to solve the problem such as the inertial information of yaw angle which is immeasurable.The two degrees of freedom vehicle mathematical model is established and the yaw angle state observer process is designed.The estimated conditions and influence factors used in the process are calculated.The numerical calculation software Matlab is combined with the dynamics simulation software Adams to establish the co-simulation environment to verify the precision of the state observer satisfy the requirements of the algorithm in the vehicle safety and stability system.