Spark-ignition　combustion　mode　could　be　used　to　widen　the　operation　range　of　homogeneous　charge　compression　ignition　combustion　mode　on　a　hydrogen-dimethyl　ether　(DME)　engine.　To　improve　power　output　and　reduce　nitrogen　oxides　emissions,　this　study　investigated　the　combustion　and　emissions　properties　of　a　hydrogen-DME　spark-ignition　engine　under　various　DME　fractions　(alpha(DME)).　The　result　showed　that　flame　development　and　propagation　periods　were　extended　after　DME　blended.　The　increases　of　both　periods　were　1.7　and　2.0　degrees　CA　when　alpha(DME)　various　from　1.4%　to　3.0%,　respectively.　However,　when　alpha(DME)　increased　to　3.4%,　flame　propagation　period　had　a　1.7　degrees　CA　reduction　because　of　the　spontaneous　high-temperature　oxidation　of　a　few　end　unburned　mixtures.　Blending　DME　could　improve　power　output　of　the　neat　hydrogen　engine.　The　maximum　improvement　of　indicated　mean　effective　pressure　could　achieve　18.3%,　after　DME　addition.　Because　of　the　weakened　flame　kernel　and　flame　propagation　process,　when　alpha(DME)　lower　than　3.0%,　blending　DME　increased　cyclic　variation　yet　the　variations　were　in　0.13%.　Nitrogen　oxides　emissions　could　be　reduced　significantly,　when　DME　was　added　into　the　neat　hydrogen　engine.　The　maximum　reduction　could　achieve　49.9%,　based　on　neat　hydrogen　fuel-supply　mode.　Hydrocarbon　and　carbon　monoxide　emissions　were　increased　after　DME　addition.　When　alpha(DME)　increased　from　1.4%　to　3.4%,　the　enhancement　of　hydrocarbon　emissions　was　about　two-third　lower　than　that　of　carbon　monoxide　emission.