The invention provides a method for judging the category of failures caused by electrical contact in a sealed electromagnetic relay. The method comprises the following steps: firstly, running tests on the reliability life of a plurality of sealed electromagnetic relays as the samples to be tested; recording the relation between the contact resistance and other characteristic parameters of each sample to be tested and the operation frequency thereof in the entire test process; forming a data matrix Xn*6 from the six characteristic parameters, such as the contact resistance; carrying out the dimension reduction pre-processing on the multi-dimension characteristic parameter data by using the principal component analysis method; extracting the corresponding data characteristics from the data subjected to the dimension reduction, and sorting the data characteristics by failure mechanisms; and calculating the Mahalanobis distances between the new sample to be tested and various training samples using the distance discriminant analysis method, and comparing the Mahalanobis distances to judge the category of the failure. Instead of opening a housing and achieving the failure analysis by optical microscopes and other instruments, the invention can eliminate the interference factors caused by other inducements and expose and locate the real causes of failures.