Vertical birotary milling head is the most important functional component of middle and large dimensional fiveaxis machining centers. When the rotation tool center point（RTCP） function is on, two rotating coordinates will cause the additional movement of the machine tool. By studying the additional movement of the machine tool, the kinematic matching relationship between the threeaxis machine tool and the two rotating coordinates was founded. The additional displacement, velocity and acceleration of the machine tool caused by the two rotating coordinates were calculated by establishing the RTCP kinematic mathematical model, and the relationship between the additional movement of the machine tool and the distance between the B axis and the tool point, the rotational speed and angular acceleration of B axis and C axis were analyzed. The research results provide reference for the research and development of fiveaxis machining center.