Disclosed is a direct-current partial discharge detection device of a converter transformer. A detection impedor is serially connected in each of a valve winding and a line winding of the converter transformer, impulse voltage on the impedors is monitored, and if polarities of the impulse voltage on the two detection impedors are opposite, a partial discharge signal is considered to exist inside the converter transformer; if the polarities of the impulse voltage on the two detection impedors are identical, an external interference discharge signal is considered. The utility model discloses a direct-current partial discharge measurement technique of the converter transformer, a blank of current direct-current partial discharge detection is filled, interference of the external discharge signal can be eliminated effectively, and the partial discharge signal inside the converter transformer can be separated accurately. The partial discharge signal is further judged by the aid of an electroacoustic combination method. Analysis determination and accurate position of partial signal occurrence are further detected by the aid of ultrasonic waves. By means of electroacoustic combination, effectiveness and reliability of detection are high.