Abstract: The ignition performance of biodiesel was redesigned by using cetane number improver-di-tert-butyl peroxide. The bench test was conducted to measure the cylinder pressure and emissions in a diesel engine at different loads at the speed of 2 900 r/min. The effects of DTBP proportion on combustion process and emissions of the diesel engine fuelled with biodiesel were also investigated. The results showed that compared with biodiesel, with the increase of DTBP content, the ignition delay and the maximum cylinder pressure were decreased. With the addition of 0.75% DTBP in biodiesel, the ignition delay was shortened by 1. 2°CA, while the combustion duration was shortened by 3°CA, the maximum cylinder pressure was reduced by 2.5%. The HC、CO and smoke emissions of diesel engine were improved significantly with the addition of DTBP. When the diesel engine fuelled with 0.25%DTBP, the emissions decreased most at rated speed and 25% load. Compared with biodiesel, HC emission decreased by 42.7%, CO emission decreased by 13.9%, NOx emission decreased by 15.7%. But with the increase of adding proportion of DTBP, the emissions would increase slightly. DTBP has no effects on the emission of biodiesel in calibration conditions.