AgCl and AgBr are a special type of superionic conductor, whose superionic phase transition does not accompany any first-order structural phase transition. In the paper, the ionic conductivity of AgBr is investigated by the first principles calculations with VASP code. The calculated results show that the isolated charged interstitial or vacancy is always more stable than the neutral one whether the system is doped or not: the interstitial hops along < 001 > direction, and the potential barrier is 0.29 eV; the vacancy hop mainly along < 111 > direction, and the barrier is 0.16 eV: the migration barrier of vacancy is obviously lower than that of interstitial, and then the ionic conductivity is mainly due to the diffusions of vacancies. Crown Copyright (c) 2009 published by Elsevier B.V. All rights reserved.