The invention relates to a harmonic source locating method and a device of a multi-feed-in AC/DC transmission system. The method comprises the following steps: 1) selecting a position of a monitoringpoint to obtain harmonic voltage and harmonic current at the monitoring point; 2) judging the type of the system in which the position of the monitoring point is located, and executing the step 3) ifthe position of the monitoring point is a DC system, and executing the step 4) if the position of the monitoring point is an AC system; 3) Based on the current direction relationship between the userside and the system side, selecting the corresponding method to determine that the harmonic source is located at the user side or the system side; 4) According to the impedance magnitude in the system, selecting the corresponding method to determine that the harmonic source is located at the user side or the system side. Compared with the prior art, the invention has the advantages of high precision, convenience in practice and the like.