The invention discloses an agricultural machine automatic navigation controller and control method. The controller is divided into two layers which are a control unit at the lower layer and an expansion unit at the upper layer. The control unit is mainly composed of a processor module based on a 32-bit ARM9 kernel, a memory module, a CAN communication module and a power management module. The expansion unit is mainly composed of universal intelligent node modules from the first to the sixth and a GPS module. The universal intelligent node modules and the GPS module are connected via a slot and a back plate of the expansion unit. The control unit and the expansion unit are connected to each other via a flat cable. The method provided by the invention mainly combines an embedded operating system, the control unit adopts a multi-tasking, event triggering design idea and a path tracking algorithm based on a fuzzy adaptive pure tracking model, and an expected wheel steering angle required for an agricultural machine to track a field path is calculated in real time so that the actual steering wheel angle of the steering wheel angle and the desired consistency to enable automatic navigation control of the agricultural machine in the field.