The single-channel absolute shaft encoder has advantages of high resolution, simple structure and strong reliability. To achieve high-precision and rapid angle identification and subdivision, this article proposes a phase-fitting-based absolute encoder angle subdivision method, which uses m-sequences to perform single-channel absolute encoding. First, the CCD sampling level signal is counted, and the combination of code values is judged to obtain the coarse code decoding data. Then, the Newton iteration method is used to implement trigonometric function fitting to obtain phase information, and a phase-based angle subdivision algorithm is proposed to obtain the subdivision angle. Finally, the angle information is obtained by combining the coarse code data and the subdivision angle. Experimental results show that the angle measurement standard deviation of the new proposed angle measurement method reaches 4. 57″, and the minimum graduation error is only 0. 23″. This method greatly improves the resolution and accuracy, and avoids the influence of the coarse error of the code disc on the angle measurement in principle.