In this paper, we propose a roll angle measurement method with a large range based on the photoelectronic autocollimator. According to the corresponding relationship between the rotation position of the measured shaft and the spot position on the circular trajectory, the roll angle is calculated quickly and conveniently using a simple algorithm. Only a mirror, a coupler and a fine shaft are contained in the measurement system besides the photoelectronic autocollimator. Aiming at the terrible measurement error induced by the axis wobbly error, two measurement schemes are proposed, which are linking the fine precision shaft to the measured shaft for reducing the axis wobbly error and using the segment measurement to enlarge the radius of the circular trajectory. The experimental results show that the measurement error is decreased by ±0.38°. The roll angle error of the mechanism is ±0.14°, and the measurement precision is about ±2′. The proposed method can be widely used in the engineering fields.