Abstract: To solve the combination problems of six DOF welding robot's inverse kinematics in complex trajectory planning,a variable step-size and revisable optimization algorithm was presented by building the nonlinear equations of robot kinematics models.Based on the conception of variable step and variable scale,the test strategy of 'forward,backward or maintain a step' was adopted to approach the optimization objective for each joint under the given error,and the precision numerical solutions could be met after iterative searches.The computed conclusion showed that this method was effective and the program was easy to design.Moreover,the numerical solutions of the inverse kinematics could be optimized in nonlinear equations.At the same time,the stationary of six DOF welding robot joint movements in complex trajectory could be guaranted.