Improving the rapidity of star identification is of great importance for improving the positioning efficiency of digital zenith camera.The traditional star identification needs to identify all the star points on each star image taken by rotation,which results in the low efficiency of star identification.Considering the existence of a common star between the star maps,a star identification method based on common stars was proposed.First,the two star images in the middle position of Positioning cycle were identified.Then,by setting up the tilt correction model,the small tilt between the CCD plane and the horizontal plane was eliminated.On the basis of tilt correction model,the Star reduction model was established,which found out the common stars between the residual star maps and the recognized star map.The experimental results showed that:The efficiency of star map recognition was greatly improved by identifying newly added stars alone.