With the aim to reveal the difference of combustion and heat release process in cylinder of engine fueled with soya methyl ester and petroleum diesel, high speed photography was used to catch combustion flame images in cylinder and thereafter the pressure indicator diagram was collected to compute the heat release rate. The combustion processes of biodiesel and petrolic diesel were illustrated in the crank angle coordinate with the direct flame images combined with analysis of heat release. Due to the contribution of bigger bulk modulus and higher cetane number of biodiesel, the beginning of injection for biodiesel was 0.7°CA earlier than that for diesel, and the ignition time of biodiesel occurred earlier 1.5°CA than that of diesel, under the unimproved conditions of fuel supply system. During the rapid combustion period, both the brightness and its lasting time of biodiesel were less than that of diesel. The heat released by the chemical reactions without obvious flame at the end of combustion only accounted for 2%~3% of the total cycle heat energy released by fuel.