The road condition can be estimated by the extended state observer and the recursive least square method based on a 7DOF nonlinear vehicle model. in which the wheel force is analyzed, the force equilibrium equation is put forward and then the second order nonlinear extended state observer is designed. The results show that the extended state observer can achieve the observation of the utilization adhesion coefficient. Then a recurrence formula is derived based on the simplified tire model. The model shows the relationship between the utilization adhesion coefficient and the peak adhesion coefficient. The peak adhesion coefficient estimator is designed based on the recursive least square method, and the Matlab／Simulink simulation results show that the estimator can identify the peak adhesion coefficient quickly. The adhesion coefficient estimator can obtain the real-time estimation accurately.