The Extended-range electric transit bus (EREbus) equipped with the auxiliary power unit (APU) using high efficient diesel engine as power source can reduce the cost of power battery and is an ideal transitional powertrain architecture to the pure electric drive. Based on chassis tests of a 12m long EREBus, fuel consumption and emission characteristics during charge sustain stage effected by temperature of the EREBus are researched. The APU of EREBus starts to work around just one point with best efficiency and lower emission when the state of charge (SOC) is too low and stop when the SOC is high, which aims to lower fuel consumption, and as a result, even during charge sustain stage, the fuel consumption per hundred kilometers of Rebus is only 22.84 L and emissions also decrease dramatically except for the ultrafine-particle number emission on account of better combustion. For the engine of EREBus there are colder engine start, severer acceleration and deceleration compared to of the traditional powered Bus, and during engine start, acceleration as well as shutdown stages of APU, there are obvious overshoots of the APU speed accompanied with sharp increases of CO, THC emissions, which is more obvious during engine start on colder condition. What’s more, on colder condition the catalyst of SCR is lighted off much earlier than on warmer condition, contributing to significant decrease of NOx emission. So on warmer condition, CO, THC, NOx and the ultrafine-particle mass emissions reduce respectively by 62.6%, 25.3%, 68.1% and 41.0% compared to on lower temperature condition, but the ultrafine-particle number emission increases by 58.7%.