The article introduced a way to accomplish the star sensor′s star extraction.First we designed the circuit system based on the DSP TMS320F206 and CPLD 1048C.Then mainly introduced the digital image processing,which included the threshold methord,connectivity analysis and the interpolation algorithm.At mean time,another improved connectivity analysis was introduced.In the end,with finishing the starsensor sample,we did a lot simulate experiments.The results proved that the new connectivity analysis method could improve the digital image procession efficiently and the star extraction method had high accuracy.