To　decrease　cyclic　variations　of　gasoline　engine　at　lean　conditions,　this　paper　investigated　the　effect　of　hydrogen　addition　on　cyclic　variations　and　lean　burn　limit　of　a　spark　ignition　engine.　Experiment　was　conducted　on　a　gasoline　engine　equipped　with　a　hydrogen　injection　system.　The　engine　runs　at　1　400　r/min,　3%　and　6%　hydrogen　volume　fractions　are　selected　to　study　the　effect　of　hydrogen　enrichment　on　engine　cyclic　variations.　Meanwhile,　hydrogen　volume　fractions　1%,　3%　and　4.5%　are　used　to　investigate　the　effect　of　hydrogen　addition　on　lean　burn　limit　of　the　gasoline　engine.　The　test　results　demonstrate　that　the　cyclic　variations　in　indicated　mean　effective　pressure,　flame　development　duration　and　flame　propagation　duration　were　decreased　under　hydrogen　enrichment.　For　a　specific　hydrogen　fraction,　the　coefficient　of　variation　in　peak　cylinder　pressure　shows　an　increasing　and　then　decreasing　trend　with　the　increase　of　excess　air　ratio.　The　corresponding　excess　air　ratio　to　lean　burn　limit　extends　from　1.45　of　the　original　engine　to　2.45　of　4.5%　hydrogen-enriched　engine.