The present disclosure provides a decomposition method based on basis material combination. In the present disclosure, a scanned object is divided into a plurality of regions, the basis material combinations used in each of the divided regions are different each other, and the scanned object is re-divided according to the re-determined equivalent atomic number of its each point until the change on decomposition coefficient meets certain conditions. Thereby, a decomposition method based on dynamic basis material combinations is realized, which reduces a decomposition error caused by improper selection of the basis material combination and improves the accuracy of the decomposition and substance identification of the multi-energy CT.