Abstract: Atmospheric refraction is a major correction term which directly influences the position measurement of celestial bodies.The existing atmospheric refraction table only adopts the average atmospheric density of observation area,while the actual distribution of atmospheric density is affected by the geographical environment,building and meteorological environment of observation station.Therefore,for highly-accurate observation,it is not enough to make correction by adopting unitary refraction table.The fundamental method to improve atmospheric refraction correction accuracy is to establish atmospheric refraction measurement model of observation station.Based on the characteristics of the multi-function theodolite,this paper proposes approach which can get the instantaneous astronomical latitude value only by using apparent zenith distance of the meridian direction.Meanwhile,we have separately established the actual atmospheric refraction measurement modal of meridional direction and multiple directions.The compiling of star-choosing program is also made to meet some conditions (??tan z→0) so that the system errors affecting the measurement of instantaneous astronomical latitude can be reduced artfully.