Abstract: By integrating pure pursuit algorithm with integral control algorithm，an autopilot method based on

discrete point set path was proposed to implement high-precision path-tracking function of a special trailer with large towed mass. The kinematic model of vehicle，the pure pursuit model，the limit steering issue and the steady-error caused by towed mass were elaborated and. Then the calculation method of target points' coordinates，the

determination method of the limit steering of vehicle and the integral control algorithm in the pure pursuit algorithm were described in detail. The experiment datasets were organized and analyzed. The results are as follows，that a special trailer with towed mass of 10 t proceeded at the maximum travel speed of 6 km/h，the maximum lateral error was 0.15 m and the average lateral error was less than 0.1 m.

      Key words: autopilot；discrete path；target points；pure pursuit algorithm