In order to achieve fast and high precision calibration of rotating structured light in the plane, a self-calibration method of rotating structured light was proposed based on the curved welding seam in space. Firstly, a camera was calibrated to obtain its internal and external parameters, weld track was pre-extracted through image processing, and the rotation axis of the steering gear was calibrated with a two-dimensional target. Secondly, the structured light was fixed to the initial pose by the steering gear head, and the plane calibration of the structured light was carried out by using the principle of constant cross ratio. The scanning welding parts of the structured light was controlled by the gantry of the rotating steering gear, and the structured light was controlled to be always perpendicular to the tangent line of the track at the scanning point. Moreover, the required rotation angle from the initial posture to the vertical posture was obtained. The self-calibration of the structured light plane at the scanning point was completed through the formula of plane rotation around any axis. Experimental results show that the plane equation of structured light is obtained by cross ratio invariant principle and plane rotation self-calibration of structured light at the scanning points, respectively. The root mean square of coefficient difference is 1.35×10-3, which has high precision and simple operation.