A realistic numerical model of a commercial diesel oxidation catalyst (DOC) was developed under an actual vehicle operating condition. To provide the material data as well as to examine the performance characteristics, conversion experiments through the DOC were performed with a 2.0 liter EGR-mounted diesel engine on a dynamometer test bench. Then, on the basis of the currently developed in-house computational code, kinetic parameters of the model reactions were calibrated through a numerical fit to the experimental data. To cover a wide range of operating temperatures, the experiments and modeling were conducted under low engine speeds (i.e., 1000 and 1500 rpm). Main objectives of this study are to develop not only a numerical model based on real-world experiments but also a methodology of how to construct it. Details of the procedure are described step-by-step in this article. Also, on the basis of the experimental results currently observed, it is proposed that additional models considering the NO2 reaction to produce NO are further required than the generally adopted DOC models to capture the negative efficiency behavior in NO oxidation at low temperatures. Because the present DOC model does not take these reactions into account, its prediction performance with experimental results at 1000 rpm is poor for NO and NO2 emissions at low temperatures but is fairly good for CO and HC emissions. On the other hand, the prediction performance at 1500 rpm is good for all of the species as well as over all of the operating temperature ranges.