Abstract: Three Dimension (3D)curve welding seam modeling is one of key technologies for seam tracking.The model can reduce the noise interference, improve the stability and robustness of welding system.Moreover, the system can obtain the fault tolerant ability from the model.The 3D curve welding seam was represented by using cubic parametric curve function, then the cubic parametric curve seam position model was obtained by using least square(LQ). Furthermore, the position model was also established by using cubic B spline approximation.The pose model was gotten by employing the position model and other welding seam coordinates.The performance of the two model was compared and analyzed.Simulation result verifies that B spline seam model excel the cubic parametric curve seam model and provid better approximation to the original welding seam.