The invention relates to a machinery automatic steering control method which comprises the following steps that: positional deviation and course deviation are determined; according to the variance in the practical front wheel rotating angle of an agricultural machine, online setting of PID parameter is completed by means of parameter self-setting PID control algorithm; moreover, the expected front wheel rotating angle of the next moment is calculated, thereby realizing automatic steering control of the agricultural machine. Based on conventional PID navigation control method, the invention makes full use of the fuzzy control method; according to the variance in the practical front wheel rotating angle of an agricultural machine, the invention meets the different requirements of the machine on PID control parameter under different errors and error change rate, thereby realizing online setting of PID parameter. The invention not only has the advantages of fuzzy control such as flexibility and adaptability, but also has the characteristics of higher precision of PID control; therefore, the invention can increase the stability and precision of agricultural machine automatic steering control and the robustness of a control system.