In　view　of　high　cyclic　variation　and　HC　emissions　of　the　lean-burn　gasoline　engine　at　idle　conditions,　an　experimental　investigation　was　carried　out　on　a　gasoline　engine　equipped　with　an　electrical　controlled　hydrogen　injection　system.　The　hydrogen　volume　fraction　in　the　total　intake　of　3%　was　adopted　through　adjusting　hydrogen　injection　duration　to　study　the　effect　of　hydrogen　enrichment　on　combustion　and　emission　characteristics　of　a　lean-burn　gasoline　engine　at　idle.　The　test　results　demonstrated　that　the　indicated　thermal　efficiency　was　improved;　flame　development　period　and　rapid　burning　duration　were　shortened　after　hydrogen　enrichment.　When　the　excess　air　ratio　was　1.3,　the　coefficient　of　variation　in　indicated　mean　effective　pressure　was　dropped　from　33.9%　of　the　original　engine　to　13.7%　of　the　3%　hydrogen-enriched　engine.　Under　idle　and　lean　conditions,　the　addition　of　hydrogen　was　effective　on　improving　HC,　CO　and　NOx　emissions　performance　of　the　SI　engine.