Abstract: With the rapid development of information technology,how to protect the security of the information not stolen and not subject to tampering or destruction,has become a hot issue in present.In order to solve this question,this paper mainly researched the interpreter of a new vigenere password algorithm.We used vigenere to determine the length of the key and the key word and plaintext.Eventually we got the new vigenere password decipher algorithm．

Key words: Vigenere password,Kasiski test method,Coincident index,Coincidence interaction index,Rrelative shift