According to the importance of the engine emission and because of the cost of the laboratory tests, it is necessary to simulate the engine via numerical methods. In this study a numerical simulation of single cylinder SI engine has been carried out to predict the internal combustion engine emission with the AVL BOOST software. The engine calibration has been performed in 2000 rpm engine speed and three loads (part load, mean load and WOT) and three compression ratios (12, 14, 16) with stoichiometric air fuel ratio. After the calibration of engine, the Lambda value is changed in range of 0.8 to 1.25 and the NOx and CO values are calculated. the results show that emission of NOx is dependent extermly to load of combustion engine but compression ratio has not very influence on this emission.unlike the NOx, the both compression ratio and load don't have any effects on CO values.