The road adhesion coefficient real-time estimation for vehicle dynamic control was investigated. Firstly, dynamic model of tire for braking was given based on magic formulation. Secondly, the related item to adhesion coefficient of the dynamic model was considered as one extended state of braking system, so extended state observer (ESO) was designed to estimate friction force between roads and tire in real-time based on the velocity of wheel and torque for braking. Adhesion coefficient was deduced. Finally, simulations were performed on uniformity road and varied road. The simulation results showed this method was robust to parameters perturbation of braking system and sensor noise, it could estimate adhesion coefficient exactly in real-time. Observer was separated from controller design. 