Adopting the Di-tertiary-butyl peroxide as the additive, the starting-up performance of a compressed ignition natural gas engine was studied experimentally. The results show that the starting-up performance of engine is improved by adding certain Di-tertiary-butyl peroxide additives. During starting-up, if the mass fraction of Di-tertiary-butyl peroxide additive reaches to 14.2%, engine ignition can be realized at ambient temperature with a glow plug of 750℃. If the glow plug temperature reaches to 1120℃, engine ignition can be realized at ambient temperature with a mass fraction of Di-tertiary-butyl peroxide additive below 6.7%. However, an excessive additive will lead to the engine knocking.