In order to further improve the reliability of three-level inverter,a method of fault feature extraction using 3D graphics was proposed.Taking T-type inverter as the research object,by measuring each phase voltage of the T-type inverter output,A,B, C three-phase voltage waveforms were gotten.The three-phase voltages were use to render 3D elliptic ring.Through calculating three- dimensional circles center,mean radius and the mean and standard deviation of the deviation vector,the fault characteristic values were obtained.After using Harris hawk optimization (HHO)algorithm to optimize support vector machine(SVM) classifier parameters,the single and double tube faults of T-type inverter could be accurately diagnosed.Finally,the effectiveness and accuracy of the proposed feature extraction and fault diagnosis method were verified by simulation experiments.The experimental results show that the proposed method is simple in calculation and has high accuracy in fault diagnosis.