With　the　population　of　information　technique　and　Web　application,　Web　information　retrieval　has　became　an　essential　part　of　work,　study　and　life.　As　the　problems　of　retrieval　increasing,　many　researches　pay　more　attention　on　retrieval　technique.　The　study　presented　in　this　paper　proposes　the　query　expansion　technique　based　on　ontology.　It　uses　the　rich　semantic　knowledge　of　ontology　to　upgrade　the　retrieval　based　on　keywords　to　concepts,　and　combines　it　with　the　specialized　engine　to　improve　retrieval　effect　and　efficiency.　The　paper　also　takes　patent　information　for　example　to　explain　its　application　at　the　end.　©2009　IEEE.