The invention discloses a frequency converter fault diagnosis method. The method includes the following steps that: step 1, circuit simulation is performed on a frequency converter; step 2, waveform images are obtained in a fault simulation circuit, and corresponding features of each image are extracted through a feature extraction method; step 3, a Bayesian classifier is constructed, the distribution model of the image features is determined; and step 4, the data in the step 1 to step 3 are summarized, so that fault database data are built. According to the method of the invention, a computersimulation method is adopted to perform fault simulation, and therefore, the efficiency and quality of work can be improved; when the frequency converter actually fails, it is unnecessary to check equipment one by one, instead, the position and cause of the fault are quickly judged according to law results obtained by previous fault simulation, and therefore, maintenance can be carried out in time.