Abstract: Based on the on-site detection requirements of winding current and generation mechanism of the harmonic current in the converter station, this paper presents a system for detecting harmonic current in the grid side windings of the converter transformer to obtain the winding current harmonic and analyzes its influence on power loss, internal temperature rise and vibration noise of the transformer. The technologies of current signal extraction, signal synchronous acquisition, optical fiber transmission, and harmonic cluster frequency algorithm are combined in the winding harmonic current detection system. Under the steady-state operation condition of bipolar equilibrium constant power, the effectiveness of the detection system is verified by the results of on-site detection and the simulation analysis of the harmonic characteristics. Based on this, the harmonic current of the grid side winding is detected and analyzed during the process of dc transmission power rise. The results show that, with the increase of DC transmission power, the distortion rates of 11th, 17th, 19th, 23rd, 29th, 31st, 35th, 37th, 41st, 43rd, 47th and 49th harmonics have a significant decline trend, and the total harmonic distortion rate reduces gradually.