In order to solve the problems such as high dimension of encrypted key

low degree of update flexibility and low search speed in the field of encrypted search

we propose a novel classificatory group index method-CGIM.The method extracts category keywords from classified data to create group index

and uses group encryption method to transform a high-dimensional secret key into several low-dimensional keys to reduce the encryption time of indexes and query requests.In addition

each group in the index is corresponding to different category.Thus

the method can not only achieve classification update to improve the flexibility of document update

but also can generate a targeted trapdoor in the retrieval process to improve the search speed and efficiency further.Through security analysis and performance test

we prove that the method is feasible and effective.