Abstract: In order to investigate the emission characteristics of heavy-duty liquefied natural gas vehicle on real-world roads, real-world driving emission tests were performed on two China Ⅴ and two China Ⅵ heavy-duty vehicles using a portable emission measurement system (PEMS). The CO and NO_x emission characteristics were analyzed. The results show that the high emission areas of CO and NO_x for China Ⅴ vehicles on three types of roads (urban, rural, motorway) are mainly distributed under acceleration conditions of the low and medium speed. While high CO and NO_x emission areas under urban and rural conditions of China Ⅵ vehicles are mainly distributed in the range of speeds greater than 30 km/h, and high CO and NO_x emission areas under motorway conditions are discretely distributed. Notably, there are high NO_x emission areas under deceleration conditions with high speed. After dividing the vehicle specific power (VSP) bin according to the MOVES model, it is found that when driving condition bins in Bin11-18, CO and NO_x emission rates of China Ⅵ vehicles are stable and maintained at a low level. In Bin21-28, with the increase of VSP, CO and NO_x emission rates of China Ⅵ gradually increase. Comprehensive emission factors of CO and NO_x of China V vehicles are 1.1-3.9 and 3.3-8.2 times higher than those of China Ⅵ vehicles, respectively, and emission factors of CO and NO_x under urban conditions are 3.0-25.0 and 11.3-30.2 times higher than those of China Ⅵ vehicles. NO₂/NO_x ratios of China Ⅴ vehicles are much higher than those of China Ⅵ vehicles. But NO₂/NO_x ratios under motorway conditions are lower than those under other road type conditions. Compared with the results of other studies, it was found that the CO and NO_x emission factors of China Ⅵ heavy-duty vehicles were higher than those of China Ⅵ heavy-duty diesel vehicles. The study shows that CO and NO_x emission factors of China Ⅵ vehicles are lower than those of China Ⅴ vehicles, and the difference is more obvious in urban roads.