When diesel engines operate at regions with different altitudes, there are differences between their operation properties. The properties of diesel engines at different atmospheric pressures have been studied by means of a micro-computer controlled atmosphere-simulating system. The properly differences of the diesel engine between different atmospheric pressures have been analyzed in detail. Some new dimensionless parameters have been set up to analyze the operation properties of diesel engines at different atmospheric pressure. The conclusions contribute to analyzing and improving the properties of diesel engines at regions with different altitude, and remodify the standard of the atmospheric amendment for diesel engines.