The invention provides a vehicle non-steering left rear wheel linear speed estimation method based on a sliding-mode observer, wherein the method is suitable for estimating the linear speed of a left rear wheel of a four-wheel automobile with front wheels being steering wheels and rear wheels being non-steering wheels. The method includes the steps that a wheel dynamic model is established for the non-steering left rear wheel first, the sliding-mode observer for the linear speed of the left rear wheel is designed on the basis of the model, all gains of the sliding-mode observer are determined according to the stability principle, next, the designed sliding-mode observer for the linear speed of the left rear wheel is processed through discretization, and finally the linear speed of the non-steering left rear wheel of the vehicle is accurately estimated through recursion of estimation of the sliding-mode observer. The method is high in anti-interference capacity, precision, and real time performance and low in cost.