In this paper, a simplified model of the robot (joints are spheres and connecting rods are capsules) was established for the problem that the multi-degree-of-freedom manipulator collides itself during the movement, furthermore, the collision detection problem of the multi-degree-of-freedom manipulator was transformed into an interference calculation problem between the simplified geometric model (In this article, it is called a collision detection primitive).The interference problem was further decomposed, and finally it was transformed into a minimum distance between the two spheres, between the two capsules, and between the sphere and the capsule. And an accurate and fast collision detection method was proposed to calculate the distance between the axes of two space capsules. Implementing the algorithm and applying it to a 6R series robot, finally, the joint simulation with Matlab and Adams was used for verification. The simulation result demonstrates the effectiveness of the algorithm.