The invention discloses an idle neutral control method of an automatic transmission based on feedforward PID. The fuel consumption rate of an automobile equipped with a hydromechanical automatic transmission can be effectively reduced, meanwhile, gear shifting impact in the gear shifting process can be reduced, and the comfort of the whole automobile can be improved. The control method comprises the following steps that a brake pedal position sensor, an accelerator opening sensor, a vehicle speed sensor and a transmission gear sensor always detect the running state of the automobile, after a TCU judges the state, a low-gear clutch is separated by changing the pressure of an electromagnetic valve, and meanwhile, and the control of an engine and the transmission is coordinated to complete the change from the driving gear to the neutral gear. When the TCU detects the intention of a driver to start the automobile again, the pressure of the electromagnetic valve is changed so that the low-gear clutch is gradually engaged, the change from the neutral gear to the driving gear is completed, and the whole control process is completed. The control method is applicable to the automobile equipped with the hydromechanical automatic transmission, the control of an engine idle speed system and the transmission is coordinated in a power cut-off process, and the comfort and fuel economy are good.