YN38CRD2 diesel engine was retrofitted into CNG-diesel dual fuel engine. Compared with the original engine, the power performance of retrofitted engine kept the same, but the fuel economy improved. The dual fuel engine could realize the reactioncontrolled compression ignition (RCCI), had the low exhaust temperature, and was able to switch between pure diesel and dual fuel modes easily. According to these characteristics, the performance of CNGdiesel dual fuel engine achieved the design goal.