When working in plateau environment the combustion process of diesel engine would deteriorate, and the engine performance decline significantly. In this paper, Isooctyl Nitrate(EHN) was blended in the diesel fuel as additive to improve the combustion process. The catabolism pathway of Isooctyl Nitrate(EHN) was analyzed, its mechanism was uncovered by chemical kinetics. And serial of tests were carried out on a single cylinder diesel engine bench to study the effects of EHN additive on the diesel engine combustion characteristics with the low intake pressure of 68kPa. Results showed that the generation of OH、H、HO2 and H2O2 radicals in n-heptane reaction could be promoted by EHN additive. In both stages of low temperature and high temperature, the decomposition speed of n-heptane was accelerated, which shortened ignition delay of engine combustion process. Four kinds of fuel were tested: diesel fuel, diesel fuel with 0.3%, 0.6% and 0.9% EHN of mass fraction. Compared with diesel fuel, the cylinder pressure decreased 0.06 MPa, 0.09 MPa, 0.13 MPa with different amounts of EHN additive under low intake pressure condition. The peak value of heat release rate decreased 5.0%, 8.0%, 9.8% each, and the curve of heat release rate moved forward 0.4 ºCA, 0.8 ºCA, 1.1 ºCA. In addition, engine output torque increased, while specific fuel consumption decreased. The dynamic performance and fuel economy of diesel engine were improved.