The data transmission coupler is composed of two symmetrical half-ring structures. The first part includes packaging layer, grounding part, magnetic material, windings, and connector. The second part includes packaging layer, and magnetic material. Windings are wrapped on half-ring shaped magnetic material. Two ends of the windings are connected to the connector electrically. Through structural parts of copper, body case of the connector to the grounding part. The packaging layer packages the grounding part, magnetic material, and windings into an integral body. The connector and the grounding part are exposed out of the packaging layer. The packaging layer packages the half-ring shaped magnetic material of the second part into an integral body. Two parts are put together to form an integrated ring structure. Being applicable to data transmission through metal pipes, the coupler is able to inject, pick-up, and insulate signal electrically. Meanwhile, insertion loss is lowest.