An experimental study on combustion and emission characteristics in a manifold-injection SI turbocharged HCNG engine with several HCNG blend ratios (0～50%) under a certain condition has been done. The results showed that with the HCNG blend ratio rising, the maximum brake toque timing (MBT) of the HCNG engine decreased and the indicted thermal efficiency increased. The lean operation limit was enlarged by increasing the HCNG blend ratio. The combustion duration and the ignition lag were both reduced with the HCNG blend ratio increasing. At last with raising the HCNG blend ratio, the exhaust NOx and CO raised, and contrarily the exhaust CH4 fell.