The invention discloses an analogical electronic circuit fault diagnostic method based on an M-ary-structure classifier, which belongs to the field of analogical circuit network test. The invention comprises the following steps: firstly, analyzing the testability of an analogical circuit to determine proper test stimulus and a test point; secondly, acquiring to-be-tested outputting signals at a testable node of an electronic circuit; thirdly, compressing acquired circuit fault information to extract fault characteristic samples; finally, designing the tags of the samples in an M-ary encoding way, establishing a hyperspherical sub-classifier in the way of a SVDD classifier, training the samples, and storing information to form a fault dictionary after training. The invention has the advantages of less classifiers, simple method, high reliability, and the like, thereby improving the automation degree and the efficiency of the online fault diagnosis of a power electronic circuit.