Abstract: Based on the kinematics equation and the orthogonal character of the rotation sub-matrix in a transformation matrix,an approach to the inverse kinematics problem of 6R robots is proposed.The problem is reduced to four nonlinear constant coefficient equations including only four unknown variables through vector operation,and then eight closed-form solutions can be gained by solving the four equations and other suitable additional equations.The experimental results with QJ-1 welding robot illustrate that the proposed algorithm can solve the inverse kinematics problem in only 0.087 ms,which is faster than the traditional inverse transformation method on the same experiment platform,and simulating results on planar condition also prove the effectiveness of the proposed algorithm.The proposed algorithm can be applied to 6R robot on-line control system with a strong real-time performance.