This　paper　takes　the　mean　monitoring　data　of　Wenyu　river　basin　in　Beijing　during　2006-2010　as　an　example.　Based　on　the　characteristics　of　origin　data,　the　water　quality　assessment　(WQA)　is　analyzed　by　factor　analysis,　which　focuses　on　five　aspects:　data　standardization,　applicability　evaluation,　principle　factor　extraction,　principle　factor　interpretation　and　factor　scores.　Results　show　that,　by　objectively　and　reasonably　using　the　factor　analysis　to　evaluate　water　quality,　the　development　tendency　and　variation　law　of　regional　water　quality　can　be　further　understood,　which　can　be　a　reference　for　contamination　control　planning　of　a　region　environmental　system.