To research performance of bio-oil/diesel emulsified fuels used in diesel engine, emulsified fuels with different bio-oil mixing ratios were prepared with right amount emulsifier and were fueled to a R180 diesel engine, the fuel characteristics, economy, emissions and effect to diesel engine were measured, compared and analyzed. The results indicate that bio-oil/diesel emulsified fuels are relatively steady; diesel engine can run with emulsified fuels. However, fuel consumption is more than diesel while thermal efficiency is lower; HC and CO emission increase while NO_x emission decreases. It is funded that the rubber sealing elements are a little swelled, emission changes abnormally the result of wearing and rusty atomizer after some hours of using the fules. These experiment results have important significances in further research of using bio-oil in diesel engine.