| The cold start tests of a direct inject turbocharged diesel engine with a low compression ratio of 14.25 were conducted respectively at an altitude of 0, 3 000, and 4 500 m at different coolant auxiliary heating temperatures of 20, 30, 40, 50 and 60 ℃, as well as using intake heating auxiliary, by utilizing the plateau environment simulation test bench, to study the influence of coolant heating temperature and intake heating on its start performance of the diesel engine under different altitude conditions. The results indicate that the after burn cycle with a poor work ability and the misfire cycle with negative work appear more and more frequent at a higher altitude in the cold start of a low compression ratio diesel engine, which caused the reduction of combustion work capacity, the extension of start up time, and the deterioration of starting performance with elevation increasing. When started under conditions of heating coolant or intake air, the number of after burn and misfire cycle was significantly reduced during start up, then the power ability were resumed and the engine starting performance were improved. However, the occurrence probability of after burn and misfire cycle could not be further reduced when the temperature of the coolant reached a certain degree such as 40 ℃, and a further higher coolant temperature will not be effective for improving the starting performance. Compared with intake heating, coolants heating auxiliary can both increase the temperature at the end of the compression process and reduce the friction resistance during start process at the same time, then obtain more better improvement for cold starting of low compression ratio diesel engine.