Abstract: The differences between GB15097 and IMO standard are discussed.The exhaust emission of two engines of different model is tested for a set of injection timing settings.The test results, after correction, are analyzed and compared.The tests show that for both of the engines, the NO_x specific emission goes down noticeably and PN specific emission goes up slightly when injection is retarded 2° CA.The change of HC specific emission is complex, depending upon the engine model and testing cycle.The IMO humidity correction factor for NO_x is slightly higher than GB correction.This makes IMO corrected NO_x specific emission higher.The first phase emission limit of GB standard can be complied by optimizing the injection timing of an engine without violating the PM emission limitation.