The off -line programming software, MoToSim EG of Motoman -HP20 welding robot for plans trajectory with the method of point to point, while for some complex curve, it needs a lot of point constraints to achieve higher accuracy requirement, leading to the complex programming process. Aiming at this shortcoming, a simulation platform set was developed based on MATLAB environment for a six degrees of freedom (6 -DOF) welding jointed robot to realize human -machine interaction (HMI). The experiment data communication verification was completed. Results show that the simulation platform can not only complete the point -to -point trajectory planning in joint space and right angle coordunate space, but also realize trajectory planning of arbitrarily known analytical motion, and get the trajectory data to teach and play, simplifying the complex trajectory of robot programming method, further improving the function of trajectory planning offline programming.