The　effects　of　three　methods　of　calculating　natural　gas(NG)　supply　on　engine　power,　fuel　economy　and　emissions　characteristics　were　investigated　experimentally.　The　results　reveal　that　the　influences　of　the　equal　calorific　method(ECM)　and　the　stoichiometrical　ratio-equal　air　consumption　method(SR-EACM)　on　the　engine　performance　are　relatively　slight,　and　the　differences　are　less　than　5%　at　all　working　conditions.　The　actual　air　fuel　ratio-equal　air　consumption　method(AEACM)　can　obviously　improve　the　engine　power　with　an　average　increase　of　42.33%　in　power　output.　As　the　fuel　supply　system　is　not　optimized,　the　brake　specific　fuel　consumption　can＇t　be　curbed　effectively　with　the　three　methods.　Moreover,　with　dual　fuel　working　model,　NOx　emissions　are　significantly　decreased　and　the　level　of　HC+NOx　emissions　at　medium　and　heavy　load　conditions　meets　the　regulation　requirements.　Also,　the　emission　of　CO　at　low　speed　conditions　meets　the　requirements.　©　2019,　Chinese　Society　for　Internal　Combustion　Engines(CSICE).　All　right　reserved.