The invention relates to a cylindrical mirror optical axis determination system and method. The system comprises a posture adjusting tool, a mirror frame, an optical centrescope, a CCD camera and a PC. The posture adjusting tool is arranged on a lathe rotary shaft. The mirror frame is fixed to one end of the posture adjusting tool. The optical centrescope is located in front of an emergence window of the mirror frame and connected with one end of the CCD camera. The other end of the CCD camera is connected with the PC. A cylindrical mirror is fixed in the mirror frame. The cylindrical face of the cylindrical mirror faces the optical centrescope, and a face B is opposite to the cylindrical face. The technical problems that in an existing method for determining cylindrical mirror optical axis bases, optical elements are prone to being scratched, and the optical axis bases are low in precision are solved. The optical non-contact measurement mode is completely adopted, a plane auto-collimation reflection image and a cylindrical face auto-collimation reflection image of the cylindrical mirror are found, and a film coating face of the cylindrical mirror cannot be scratched.