The invention provides a gear fault diagnosing and processing method. The method comprises the steps that when preset judgement conditions are met, estimated meshing gear judgement of shafts of odd numbers and shafts of even numbers of a speed changer is conducted; the state of a sensor at a shifting fork position is monitored, when it is detected that the sensor at the shifting fork position doesnot work, a gear meshing condition under the current working condition is judged by adopting an estimated meshing gear, and fault processing is conducted; the gear engaging and shifting motions of the speed changer are judged, when gear engaging fault exists in the speed changer, the estimated meshing gear is adopted for judging whether or not a synchronizer is damaged, and fault processing is conducted. According to the method, in the gear fault processing process, the safety and reliability of vehicle driving are ensured.