The invention discloses a 
velocity estimation and friction identification method of a four-wheel turning / driving vehicle. The 
velocity estimation and friction identification method comprises the steps that firstly, a vehicle body coordinate 
system O-XY is established; secondly, a vehicle kinetic equation is established; thirdly, a wheel kinetic equation is established; fourthly, a wheel 
velocity equation is established; fifthly, a wheel 
slip rate equation is established; sixthly, the longitudinal force and lateral force of a wheel are obtained; seventhly, a friction model is parameterized; eighthly, a kinematical equation describing the relation of the vehicle velocity, the 
yaw velocity and the acceleration is established; ninthly, an observer is designed under the situation that detectable signals z comprise the longitudinal acceleration ax, the lateral acceleration ay, the 
yaw velocity r, the wheel 
angular velocity wj and the 
steering wheel rotation angle 
delta i; tenthly, persistent excitation conditions are defined. According to the 
velocity estimation and friction identification method, the nonlinearity self-
adaptation observer for estimating the vehicle longitudinal velocity and the 
lateral velocity is established, the tire 
road surface friction parameters are established in real time according to the change of 
road surface conditions, and the velocity is estimated more accurately.