The invention provides a fault diagnosis method on the basis of the evidence theory, and relates to the field of fault diagnosis. The method comprises the steps that a triangular fuzzy model is builtfor all faults, a triangular fuzzy model is built for to-be-tested data, a basic probability assignment function is generated according to the overlapping degree between a to-be-tested module and a fault module, and basic probability assignment functions generated under all the faults through evidence theory combination rules are blended to achieve fault diagnosis. The method has the advantage ofbeing easy to compute; according to the basic probability assignment function generation method, processing on fuzzy information is well achieved; according to the fault diagnosis method, fault diagnosis of a motor rotor can be achieved.