In order to study the application of the liquefied natural gas (LNG) on diesel engine, a turbocharged diesel engine was converted into a dual-fuel engine ignited by diesel fuel. The effects of load ratio on fuel economy and emissions of dual-fuel engine were compared and analyzed at engine speed of 1200 r/min, 1600 r/min and 2200 r/min. The experimental results show that, the specific fuel consumption is reduced with the increase of load ratio at different speeds. As the load ratio increases, CO emission of dual-fuel reduces, but it increases slightly at high loads and full load. When the load ratio is less than 40%, HC emission of dual-fuel is reduced significantly with the increase of load, but increases when the load ratio continues to increase, and finally HC emission is stable. When the load ratio is less than 40 %, NOx emission is relatively low, as the load ratio increases, increases sharply, but at high loads and full load, reduces slightly.