In order to estimate the adaptability of the diesel combustor, the combustion characteristics of pure diesel and emulsions of bio-oil and diesel (with 5wt% and 50wt% bio-oil contents) were investigated by numerical simulation method. The factors including ignition delay, temperature distribution and combustion components distribution in the combustor were studied. The combustion characteristics of 5wt% bio-oil emulsion were nearly consistent with those of pure diesel. The only minor difference was that its ignition delayed slightly to the upstream. In contrast, 50wt% bio-oil emulsion had different performences in the combustor, whose ignition was shortly delayed.