For the security of information, one has to be prevent it from unauthorized user's access (confidentiality), prevent it from unwanted changes (integrity), and it should be available to its intended users (availability). Diffie-Hellman algorithm is used for secret key generation. The purpose of the Diffie-Hellman protocol is to enable two users to exchange a secret key securely that can then be used for subsequent encryption of messages. Man-in-middle attack is the main problem of Diffie-Hellman algorithm. This paper is to study and analyze Diffie-Hellman key exchange protocol. In this paper, the authors study of N-Party Man-in-Middle Attack in Diffie-Hellman key exchange protocol.