In　order　to　accurately　control　the　safe　berthing　of　large　ship,　the　characteristics　and　berthing　process　of　large　ship　were　analyzed,　the　mathematic　model　of　its　auxiliary　berthing　instrument　was　established,　and　the　berthing　instrument　and　its　display　system　of　software　terminal　were　designed.　The　two-point　position　differential　global　positioning　system(DGPS)　technology,　automatic　identification　system(AIS)　technology　and　wireless　fidelity(WiFi)　technology　were　used　to　complete　the　design　of　berthing　instrument　and　the　data　transmission,　and　the　berthing　mobile　data　including　the　relative　distances　and　speeds　between　bow,　stem　and　wharf,　the　heading　and　the　steering　rate　were　calculated,　which　were　sent　via　WiFi　to　the　software　terminal　for　the　pilots　to　guide　the　safe　berthing　and　unberthing　of　ship.　Test　result　shows　that　the　berthing　instrument＇s　horizontal　positioning　accuracy　is　60　cm,　the　speed　precision　is　5　cm·s-1,　and　the　data　refreshing　frequency　is　5　times　·s-1.