Since spark ignition engines has a large portion in emission production, recognition of the engine emissions when engine work at high compression ratios and different conditions with gasoline and natural gas could be useful to compare engine exhaust emissions in gasoline and natural gas fuel case and find the lowest emissions production condition. In the current work, an engine was set at 9 and 10 compression ratio for gasoline and natural gas fuel case. It warmed up with fuel injection at full load, three engine speeds, at certain spark advance and four equivalence ratios. Then in each engine speed and equivalence ratio, spark advance (according to the crank angle) was changed on non-knock domain with two degree per step and external results were recorded. External data included HC and CO emissions, relative air-fuel ratio (l), also internal air-flow and external torque. It was observed that the decrease of representative equivalence ratio causes the reduction of HC and CO. At equal representative equivalence ratio the amount of HC in gasoline fuel case is more than natural gas fuel case and overall increasing was estimated more than three times. Engine speed change causes variation in the amount of HC while it has no impact in the amount of CO.