The autonomous navigation operation of agricultural machinery has become an inevitable trend in domestic and international development，and path tracking control is the key to improving the control accuracy of autonomous navigation systems. In response to the problem of low tracking accuracy of conventional pure tracking algorithms when turning in complex agricultural environments, an novel path tracking control algorithm for the four-wheel synchronous turning agricultural machinery was proposed based on the improved pure tracking model. A kinematic model and a pure tracking model based on four-wheel synchronous steering agricultural machinery were established. On this basis, an improved pure tracking model was obtained by considering heading error. RTK positioning coordinates were modified, and the optimal forward looking distance was derived from the optimal target points in the forward-looking area according to the evaluation function of the quantitative error. The proposed algorithm can obtain the appropriate forward looking distance in real-time for the improved pure tracking model of four-wheel synchronous steering agricultural machinery, which minimized heading and lateral errors and achieved adaptive optimization of target point. The simulation results showed that the average absolute lateral error of the method during turning was reduced to 0.035m, and the average absolute heading error was reduced to 0.212°. The paddy field experiment showed that when the operating speed of the four-wheel synchronous steering agricultural machine was 3.6km/h, the average absolute lateral error of the four-wheel steering agricultural machine trajectory tracking was reduced to 0.109m, the average absolute heading error was reduced to 2.799°, and the turning tracking accuracy was significantly improved.