Abstract: Objective Aimed at the problems of low welding efficiency and high risk of high-altitude operation about Y-joint of deep-water jacket, this study proposed a fully automatic multi-layer and multi-pass welding path planning method based on six-axis robot. Methods Firstly, based on the dynamic characteristics of the groove morphology of Y-joint branch pipe, parameter equation of intersecting line and calculation model of dihedral angle were established. The geometric relationship between groove angle and theoretical cutting angle was deduced. The three-dimensional theoretical model of intersecting line weld and groove was constructed, and the variation law of groove angle along weld was analyzed. Then, according to the equal height filling strategy, the welding process was planned by controlling the number of layers and dynamically allocating the number of passes, combining with the coordinated control of welding speed and wire feeding speed. Results The method realized self-adaptive path planning of variable cross-section groove and process planning. Conclusion This method significantly improved the welding efficiency and process stability, and provided theoretical support and engineering practice reference for the automatic welding of complex nodes in marine engineering.