Open　domain　question　answering　(QA)　has　drawn　much　attention　from　the　natural　language　processing　communities.　A　pattern　based　question　answering　system　is　introduced,　and　the　deep　performance　analysis　and　the　evaluation　of　the　QA　system　are　presented.　The　impact　of　parameter　tuning　and　training　set　size　on　system　performance　is　discussed　as　well.　Meanwhile,　the　t-test　results　denote　the　significance　of　the　performance　improvement　by　different　factors.　Natural　language　processing　tools　are　used　in　the　QA　system,　such　as　the　syntax　parser　and　the　named　entity　recognition　tool.　Analysis　results　indicate　that　these　tools　play　an　important　role　in　the　QA　system.