This　paper　presents　a　group-based　reputation　mechanism　and　gives　a　distributed　implementation　method　for　mobile　p2p　networks.　In　the　proposed　mechanism　peers　with　similar　mobility　are　clustered　into　a　set　of　groups,　where　there　are　two　different　kinds　of　peers:　Mobile　and　Power　peers.　Mathematic　analyses　and　simulations　show　that　the　adoption　of　group　avoids　the　communication　overload　in　global　trust　computation,　and　the　benefits　of　trust　evaluation　are　maintained　by　managing　trust　in　the　groups.　Compared　to　the　current　p2p　reputation　mechanisms,　the　proposed　mechanism　is　slightly　affected　by　the　dynamic　joining　and　departing　of　peers.　Additionally,　it　effectively　encourages　new　peers　to　take　part　in　the　systems　actively　and　friendly.