Objective: Telescopic optical axis change (OAC) is the biggest source of systematic error of astrometry. Real-time determination and calibration of OAC are the foundation of obtaining high-quality astrometric data. Determination and analysis the influence of OAC on time and latitude measurements should be done to meet the requirement of high-quality astrometric results. Method: First

the influences of OAC on time and latitude measurements are analyzed. The method of determining OAC for Multi-function Astronomical Theodolite is introduced. Then we determine the OAC in real time and analyze the results. Result: Experimental results indicate that the influence of OAC on latitude measurement can reach to 2.5" when the zenith distance is 550

and the precision of latitude measurement can reach 0.36" from 1.37" after the calibration of OCA

the precision of time-measuring can reach 0.023s from 0.033s after the calibration of OCA. Conclusion: The precision of latitude and time measurements is significantly improved and can satisfy the requirements of high-quality astrometry after the measurement and calibration of OAC in real time.