Abstract: At present, the method for position sensor calibration of zero and full point of cylinder valve servomotor in Jinping Hydropower Station Ⅱ is defective, possibly resulting in alarm of the super nut or cylinder valve stuck. Therefore, the study for new method of zero and full point calibration was carried out. A new calibration method is introduced, in which the offset is not adjusted, and the zero and full positions are marked at fully open or fully closed positions of cylinder valve. The position sensor calibrated by the new method are characterized as less difference, bigger tolerance and better synchronous performance, and the sensors have withstand test of long-term operation and running. So it can be used as reference for the design of similar cylinder valve systems.