A measurement method for angular positioning error of a rotary axis based on fiber laser autocollimation was proposed. An error model was established including the motion errors of the rotary axis and the installation errors. By simulating and analyzing the impact of these 23 errors on measuring angular positioning error, the results showed that only four installation errors between the reference and the target rotary axes have influences depending on the rotation angle of the rotary axis. And only the two angular errors need to be made fine adjustments to insure that the influences were less than 0.2″. The angular positioning error of an indexing table was measured by the measuring device built. The repeatability value for measuring three times was about 0.9″, and the maximum comparison deviation from the optoelectronic autocollimator was about 0.6″. The results show that the angular positioning error of rotary axis can be measured high accurately with a full-circle measuring range by using the method and device, and the proposed model is verified.