A controllable mechanism type welding robot with ten connecting rod is designed, which have five degrees of freedom (5DoF). ADAMS software was carried out on the robot mechanism of rigid body and flexible body modeling for the characteristics of the low center of gravity to mechanism and the actual working condition of the welding process，at a constant speed in a straight line welding trajectory，the simulation of different welding speed was done. The welding robot controlled mechanism with the rigid body and flexible body characteristics of the displacement change over time at the end of the welding torch are analyzed to get the change rule of welding robot to welding precision and welding speed.