An improved star identification algorithm based on the traditional triangle method is proposed in this paper to overcome the low character dimensions and high percentage of redundant matches in star identification.When a triangle is recognized by a labeling method,the fourth star is introduced as a vertex to make up a tetrahedron with the triangle,and the accessorial angular distances among them can be used not only as the supplementary character to reduce redundancies,but also to verify whether the result is correct.The proposed algorithm takes the angular distance as the main identification character and relative magnitude information as the assistant character,so that the capacity of guide star database decreases to 0.4 Mb.During star-pair matching,the hashing search is used to construct the function for identification characters to reduce travelling times and time consumption for the guide star database and to speed up the identification process,and the average identification time is 0.43 ms.The result of simulation demonstrates that the improved identification algorithm has advantages of high identification efficiency and short identification time in the all-sky autonomous star identification.