The　construction　of　urban　ecological　security　is　much　concerned　with　the　continuous　urbanization　process.　This　paper　established　an　urban　ecological　security　evaluation　system　by　employing　PSR(Pressure-Status-Response)　method,　on　the　basis　of　the　previous　studies　about　ecological　security　evaluation　by　other　researchers.　The　weight　of　each　index　was　defined　utilizing　the　AHP(Analytical　Hierarchy　Process)　method,　and　the　situation　of　ecological　security　in　Beijing　during　2000-2004　was　evaluated.　The　result　shows　that　ecological　security　of　Beijing　during　this　period　lie　in　the　situation　of　＇relatively　not　secure＇,　and　the　main　contribution　factors　are　water　resources　of　great　pressure　and　undesirable　air　quality.　©　2011　IEEE.