Aiming at the problem of high fault rate and unperceivable working fault, a fault diagnosis alarm system for the combine harvester was introduced. PLC and display were the control terminals in the system. The PLC collected the signals in the operation process such as feed-in screw conveyor, conveying channel, threshing cylinder, transporting auger, cleaning loss and attachment loss, then calculated and treated in the manner of fault diagnosis subroutine based on the trend of the signals. The test showed that the fault diagnosis method could realize the early warning for the combine and improve the working quality and efficiency of combine harvester.