In　the　view　of　low　thermal　efficiency　and　high　emissions　of　spark　ignition　(SI)　engines,　this　paper　investigated　the　effect　of　hydrogen　blending　at　intake　ports　to　an　SI　engine　on　improving　its　economic　and　emissions　performance.　The　experiment　was　carried　out　on　a　modified　4-cylinder　SI　engine　on　which　hydrogen　could　be　injected　into　the　intake　ports　sequentially　via　an　ECU　(Electronic　control　unit)　based　control　system　and　mixed　with　gasoline　on-line.　The　combustion　and　emissions　characteristics　of　a　hydrogen-blended　IC　engine　were　investigated　under　the　conditions　of　1500　r/min　and　the　stoichiometric　equivalence　ratio　with　four　different　hydrogen　volumetric　fractions　of　1%,　1.5%,　2%,　3%.　The　test　results　demonstrated　that,　compared　with　the　original　engine,　the　brake　engine　thermal　efficiency　was　increased　by　3.23%　and　the　cycle-by-cycle　variations　of　the　peak　in-cylinder　pressure　was　reduced　by　3.18%　on　average　at　the　hydrogen　addition　fraction　of　3%.　Ignition　delay　and　the　rapid　burning　duration　were　shortened;　the　peak　in-cylinder　pressure　was　increased;　CO2　and　HC　emissions　were　obviously　lower　with　the　increasing　fraction　of　hydrogen　in　the　intake.　However,　NOx　and　CO　emissions　were　also　increased.　In　a　word,　the　addition　of　hydrogen　to　a　gasoline-fuelled　IC　engine　is　a　good　way　to　improve　engine　performance.