A saddle-shaped curve is formed by intersection of two tubes. This paper proposes a new saddle curve interpolation algorithm for automated welding system with non-Cartesian coordinate system. The trajectory interpolation of saddle-shaped curve is usually carried out through approximating the curve as segments of straight line/circular arc for intersection seam automated CNC welding. Simulation of the direct interpolation algorithm is carried out to testify its effectiveness and superiority. With this algorithm, it is demonstrated that the chord error is within the allowable limits and the algorithm has high reliability.