Telescopic Optical Axis Change (OAC) is the main source of systematic errors in astrometry. Real-time determination and calibration of OAC are the foundation for obtaining high-quality astrometric data. The determination and analysis of the influence of OAC on time and latitude measurements should be performed to meet the requirements of high-quality astrometric results. First, the influence of OAC on time and latitude measurements were analyzed. The method of determining OAC for multifunction astronomical theodolite was introduced. Then, we determined the OAC in real time and analyzed the results. The experimental results indicate that the influence of OAC on latitude measurement can reach to 2.5" when the zenith distance is 55°. The precision of latitude measurement can reach 0.36" from 1.37" after the calibration of OCA. The precision of time measurement can reach 0.023 s from 0.033 s after the calibration of OCA. The precision of latitude and time measurements significantly improved and can satisfy the requirements of high-quality astrometry after the measurement and calibration of OAC in real time.