Abstract: In the west Qilian orogenic belt of Changma, Gansu,Late Sinian fossils,e.g: Leiosphaeridia,Lophosphaeridium,Cymatiosphaera,Retisphaeridium,Synsphaeridium,Multiplicisphaeridium,Retinarites et al. were discovered in Heicigou Formation of the Middle Cambrian through 1:50 000 geological mapping.Based on this reseach,the Middle Cambriam strata was divided three parts:Late Sinian strata,Early Cambriam strata,and Heicigou Formation of the Middle Cambriam and structural evolution model from the Late Sinian to the end of the Middle Cambrian was put forward.