Abstract: In order to study the effect of diesel fuel quality on a diesel engine, China Ⅲ diesel, China Ⅳ diesel and Beijing Ⅴ diesel were used, and the load-performance tests were carried out on a JX493ZLQ3 diesel engine. The revolution was set at 2 000 r/min, and the throttle opening was set at 20%, 35%, 50%, 65%, 80%, 90% and 95%, respectively. The effect of diesel fuel quality on fuel economy and emission characteristics of the diesel engine were compared and analyzed. The results showed that without any changes to the engine, diesel fuel quality could influence the fuel economy. The effect on CO and HC emissions was not obvious. Diesel fuel quality had obvious effect on NO_x and PM emissions, and China Ⅲ diesel caused relatively high emissions.