To provide a modeling method which can attain a high precision and a high reliability in simulating a coal gasification process or a coal combustion process and in predicting and evaluating various phenomena occurring in a coal gasifier or a coal combustion furnace by a numerical fluid analysis, and to provide a simulation system using the same.

In simulating the coal gasification or combustion process, the feedstock is coal, and the gasifying agent used or the oxidizing agent used is either water or air. The coal gasification or combustion process is modeled by assuming that the composition of the volatiles released is a pseudo-component CHxOy, when coal particles are thermally decomposed in the gasification or combustion.