The invention relates to a real-time estimation method of a road adhesion coefficient under a braking working condition. According to the real-time estimation method disclosed by the invention, a two-wheeled vehicle braking dynamics model, an ideal braking torque controller and a road adhesion coefficient observer are adopted, wherein the two-wheeled vehicle braking dynamics model consists of a full vehicle model and a tire model; based on the two-wheeled vehicle braking dynamics model, a saturation function and an integral switching surface are adopted to redesign a sliding mode controller, so that a shake problem is solved, and the ideal braking torque controller is set up. Based on the two-wheeled vehicle braking dynamics model and the ideal braking torque controller, a second order linear extended state observer is adopted to design the road adhesion coefficient observer and to observe an extended state quantity which is relevant with an adhesion coefficient, and then the real-time estimation of the road adhesion coefficient is completed. According to the real-time estimation method disclosed by the invention, the quantity of design parameters is small, the calculating efficiency is high, and the modes of the saturation function and the integral switching surface are adopted to solve the shake problem which is controlled by a sliding mode variable structure; the road adhesion coefficient observer adopts the second order linear extended state observer, so that the robustness is strong.