A password-based dynamic group key agreement protocol from tripartite Diffie-Hellman using pairing on elliptic curve is presented in this paper. In this scheme, due to all users share a common pre-distributed password, the setup of the key agreement is simplified and the performance is improved. In addition, each user establishes a relation between his left and right neighbors respectively in order to implement the fast joining and leaving operations. Under the DDH assumption, proofs are given to show that the proposed key agreement protocol is secure against passive attack.