Abstract: To solve the problem of traditional exploiting modification direction （EMD） methods’s limited secretinformation expression range and security, an EMD（n,m） model based on basis-free vector and EMD（n,m） model based steganography method were proposed. Firstly the embedding adjustment table was formedby calculating all m out of n carrier data combinations and then one row was selected from the secret embeddingadjustment table to embed the corresponding secret information. To further increase security, thevariables n and m were randomly generated by user keys and chaotic map, meanwhile secret bits were interceptedand the secret embedding adjustment table was scrambled. Theory and experimental results show thatby comparing with the traditional EMD, EMD （n,m） model avoids the limited scope of the basis vector andmaximizes embedding capacity, meanwhile enhances the embedded information security by adding carrierand keys related procedures for embedding or extracting secret information.