This paper proposes a leader-follower formation method for unmanned ground vehicles under which there is no need to exchange information by communication between leader and following vehicles. Based on the measurement of relative information, such as distances, orientations and velocity, by monocular camera and laser scanner mounted on the following vehicle, the formation is formed by recognizing the leader vehicle and tracking its trajectory normally. If the detection of the leader vehicle in monocular camera fails, an on-line estimator based on kinematical constraint and Kalman filters are designed to guaranteed the measurement of the leader continuously in a hundred of milliseconds time scale. The experimental results under complex traffic environment verify the feasibility and validity of the proposed method.