Abstract: The combined-adjustment principle of a two-step adjustment mechanism for the feed support system of a large aperture radio telescope is analyzed from the point of view of kinematics. The mathematical model used for the kinematic control is derived through a spatial vector method. The control scheme of fine-adjustment mechanism and the control strategy are presented, so also are the hardware configuration and the software flow of the Stewart fine-adjusting mechanism. The whole control system of the telescope feed support is also reviewed. Analysis of the combined-adjustment principle is a beneficial exploration in improving the operating accuracy of the telescope and is of use in the development of the project.