Abstract: D-H notation method and screw theory method are used to set up the kinematics model of robots when its inverse kinematics is to be solved. D-H notation method is widely used in kinematics analysis of robots, but, because D-H parameter method needs to establish coordinate system at each joint, it is more complicated to establish model. In screw method, the coordinate system of each link is established relative to the base, establish model is more convenient and the geometric meaning is clearer. The inverse solution of the kinematics model based on screw theory is usually solved by Paden-Kahan sub-problem method. Aiming at the 6R modular manipulator, the last three joint axes of the manipulator intersect at one point, this paper set up the kinematics model of the manipulator based on the screw theory. The inverse kinematics of the manipulator is solved by using the geometric relationship and Paden-Kahan sub-problem, and the analytical solution of the manipulator was acquired. The kinematics algorithm program was programmed by Matlab which verifies the correctness of the inverse solution algorithm.