Abstract: This paper introduces a fast repair methods of Versa HD volume-modulated accelerator's high voltage circuit fault:the key points test method. To identify five key points:①Enter maintenance mode to check for AFC deviation; ② The magnetron waveform MI and PFN waveform PFN V are detected on the maintenance terminal board; ③ Detect thyratron waveform; ④ Check the supply voltage of thyratron; ⑤ HT PSU 600 V DC test 600 V normal or not. The waveform or voltage is also measured to efficiently narrow the fault range to find out the cause of the fault, quickly remove the fault.