"With the rapid development of domestic industry, there has an increased in the numeber of people paying attention to environmental pollution which caused by engine emission. The technology of double fuel engine has been hignly valued by different countries in the world. Double fuel engine is a kind of engine which can not only use two fuel, but also use alternative fuel, instead of gas and petrol. In addition, one of advantages of using alternative fuel is it could decrease polloution released by engine efficiently. Due to the benefits that the double fuel engine has several characteristic includes hign efficiency, environmental protection, easy to control, this technology becomes LNG board development mainstream direction soon. In this article, it will discuss the original principle of double fuel engine structure and analyse its features. Diesel- gas double fuel is an engine that is based on diesel engine with gas fuel control system, which makes it possible to work both by small bore diesel engine and another operating mode that transfer diesel to gas. What is more, by comparing with traditional diesel engine, it can be known the disadvanges and advantages of double fuel engine better and people can be able to analyse if the technology of double fuel engine can be used widely in the board area.