Abstract: To investigate the emission characteristics of heavy-duty liquefied natural gas (LNG) vehicle on real world roads, two China V and two China VI heavy-duty LNG vehicle were sampled on real world driving emission tests using a portable emission measurement system (PEMS). 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 under three types of roads are mainly distributed in the acceleration condition of the low and medium speed. While high CO and NO_x emission areas in urban and rural conditions of China VI vehicles are mainly distributed in medium and high speed, and high CO and NO_x emission areas in motorway conditions are discrete distribution.  and more in motorway conditions. Notably, there are high NO_x emission areas in deceleration conditions with high speed. When driving condition bins in Bin11~18, CO and NO_x emission rates of China VI vehicles are less affected by the change of Vehicle Specific Power (VSP), 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 1.1-4.0 times and 3-10 times higher than those of China IV vehicles, respectively, and emission factors of CO and NO_x in urban conditions are 2.9-11 and 12-30 times higher than those of China VI vehicles. The gap is reduced and the emission factor of CO of China V vehicles is even higher than that of China VI vehicles in motorway. NO₂/NO_x ratios of China V vehicles are much higher than those of China VI vehicles. But NO₂/NO_x ratios in motorway conditions are lower than those in 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 LNG vehicles were 2.3-5.4 times and 5.2-9.3 times higher than those of China VI heavy-duty diesel vehicles. The emission factors of China VI heavy-duty vehicle of two fuel types should continue to be studies.