As the precision of a photo-turntable control system using rotary inductosyn depends on the dynamic angular position measuring precision of a rotary inductosyn,this paper explores the system error of the rotary inductosyn.The error mechanism of rotary inductosyn was analyzed,and the system error of the rotary inductosyn was quantitatively and dynamically measured by using an experimental platform.Finally,the system error model of the rotary inductosyn was put forward based on the data processing and error mechanism,and the output signals from the rotary inductosyn were compensated by the error model.The software compensation method was verified and the experimental results for the rotary inductosyn with 720 poles,12 bits show that the dynamic angle measurement accuracy is improved from 11.25″ to 1.17″,while the angular velocity estimation accuracy is improved from 0.72(°)/s to 009(°)/s.The test results show that the proposed method improves the dynamic measuring accuracy of the rotary inductosyn significantly and satisfies the accuracy demands of photoelectric platform pointing control systems.