Tests　are　carried　out　on　a　four-cylinder　gasoline　engine　equipped　with　an　electronically　controlled　hydrogen　injection　system　to　study　the　effects　of　ignition　timing　on　engine　performance　when　gasoline　is　blended　with　hydrogen.　During　tests　engine　speed　is　fixed　at　1400r/min,　and　in　hydrogen　blending　condition　the　hydrogen　volume　fraction　in　total　intake　mixture　is　kept　at　3%　by　adjusting　hydrogen　injection　pulse　width.　Meanwhile,　gasoline　injection　pulse　width　is　also　adjusted　to　make　excess　air　coefficient　maintain　at　1.2　for　both　W/WO　hydrogen　blending　conditions.　The　test　results　show　that　compared　with　original　engine,　when　gasoline　is　blended　with　hydrogen　the　ignition　timing　for　maximum　mean　effective　pressure　retards,　the　duration　of　combustion　reduces,　HC　and　CO　emissions　lowers　and　NOx　emission　increases　with　same　ignition　timing.　In　hydrogen　blending　condition,　when　ignition　timing　advances　combustion　speed　obviously　increases　with　a　same　variation　trend　of　emission　as　original　engine:　HC　and　NOx　emissions　rise　and　CO　emission　lowers.