Abstract: In order to evaluate the efficiency of the diesel engine 6V150 based on the second law of thermodynamics, corresponding analyses are carried out by exergy loss calculations on a quasi-dimensional engine model built up in software package BOOST. On the engine model validated by experiment, the data desired by thermodynamic analysis for each component of the engine are computed by the code as an interface of the BOOST. Finally, characteristics of the engine exergy loss distribution are discussed and methods of improving the efficiency of the diesel engine are proposed.