Abstract: Aiming at the problem of precision large-thread machining of the front and rear shells of a certain segment of carrier rocket, the precision large-thread structure of the front and rear shells is firstly analyzed. Secondly, research on precision machining technology of large-thread is carried out aiming at precision control of half of thread angle and middle diameter value, precision control of screw pitch surface roughness, and precision control of screw pitch cumulative error. At last, the problem of large-thread in-situ measurement is solved. It is proposed that steel ball method is used to measure the thread diameter of the front shell, three-pin relative method is used to measure the thread diameter of the rear shell, and the reasonable medium diameter interference from precisely controlled thread diameter value is used to control the final butt torque platform value.