Abstract: This paper proposes a high precision absolute time-grating angular displacement sensor with a coprime number of measurement periods. An incremental sensor with M measurement periods is added on the basis of a time-grating angular displacement sensor in the single-ring incremental electric field with N measurement periods so as to achieve combination measurement, among which two period numbers N and M of the incremental sensor are coprime numbers. The one with more measurement periods is used as the precision measurement component to improve the measurement accuracy, the one with fewer measurement periods is used as the rough measurement component, and the absolute angular displacement of the sensor is measured by using the corresponding relationship between the phase difference of the output traveling wave and the spatial angle of the two incremental sensors. The measurement accuracy is ensured by adopting a differential induction electrode structure to eliminate common-mode interference. This sensor with combined coprime numbers of measurement periods can not only easily realize absolute positioning, but also ensure a high accuracy of the sensor. A sensor prototype with an outer diameter of 154 mm, an inner diameter of 100 mm and a thickness of 2 mm is manufactured through the printed circuit board technology. The experimental platform of the sensor is built, and the prototype is tested. The test results show that the original accuracy of the sensor can reach ±1.8 in the whole circumference measurement range.