Abstract: In order to improve measurement efficiency in visual guiding theodolites, a precise guiding method based on camera optical axis was put forward. After calibrating the double-theodolite measuring subsystem and vision guiding subsystem , the system was guided initially according to the theoretical design of workpiece modulus file. Then by using digital image processing technology, the characteristic center point of the camera filed of view was distinguished and the relationship between the characteristic center point and the image center (i.e., the camera optical axis) was obtained so that vision measurement subsystem can be guided to point the characteristic center precisely. According to the calibration relation, the angular deflection between both theodolites was obtained and the theodolites were made to intersect at the target point precisely. The results show that the method can make sure automatic measurement accuracy of the system at 0.3mm and improve measurement efficiency of the system.