This study aims at real-time measurement /reconstruction of the specular three-dimensional (3D) weld pool surface under strong arc in gas tungsten arc welding (GTAW). A vision-based sensing system is used to project a dot-matrix laser pattern on the weld pool surface which is able to specularly reflect the laser pattern. This reflection pattern, deformed by the weld pool surface has been utilized to reconstruct the 3D shape of the weld pool surface. Based on careful analysis, the underlying reconstruction problem is formulated mathematically. An analytic algorithm is proposed resulting in the weld pool surface be reconstructed in real-time on average in 3:22 milliseconds. In order to verify the effectiveness of the proposed reconstruction algorithm, it is tested on objects with a priori knowledge of geometry having a specular surface. Then the robustness of the proposed reconstruction scheme is further validated using a real-time experiment.The detailed analysis of measurement error validates the accuracy of the proposed algorithm.