To assess the gaseous and particle emission characteristics of a city bus equipped with DOC+CDPF after-treatment fueled with diesel and biodiesel with 5% blend ratio while the driving distance increases, a study has been performed using portable emission measurement.The results show that the decreasing amplitudes of CO, THC, and PM increased first and then decreased with the increase of mileage. The degraded amplitude of THC continuously enhanced before 25000km, and then decreased. It became lowest at 80000km, which was 41.05% lower than the first test. The decreasing amplitudes of both CO and PM continuously increased before 35000km, and then decreased. The degraded amplitudes of CO and PM were respectively 20.24% and 11.74% at 80000km. The reduction of NO_x and PN both showed the downward trend with the increase of mileage. The reduction amplitudes of NO_x and PN both became lowest at 80000km, which were respectively 33.83% and 10.35% lower than the first test. The gaseous and particle emissions emitted from the city bus fueled with B5equipped with DOC and CDPF increased obviously at around 80000km, and the decreasing amplitudes were sharply down, so the DOC+CDPF after-treatment should be maintained to extend life cycle and reduce emissions.