The invention relates to a convertor detecting method, including the following steps: the convertor is connected with an adjustable power supply; a rated input voltage, current and a reduced proportion of the proportion relation between control parameters are preset in the convertor; the adjustable power supply is adjusted to lead an actual input voltage of the convertor to be the multiple of the reduced proportion of the rated input voltage; the actual input voltage, current and control parameters are magnified according to the reciprocal multiple of the reduced proportion to control the convertor; the working state of internal parts of the convertor is detected. The invention provides the convertor detecting method and a system to find hidden troubles resulting in failure as much as possible before accessing a high voltage power supply so as to reduce the risk of detection under high voltage.