Sustainable energy production through conversion of biomass has recently found growing interest. Among thermochemical conversion techniques, gasification is of interest to replace direct combustion emitting air pollutants that threaten our environment. However, gasification process is still far from being efficient since most of the research studies have only focused on experimental implementation of the methods while numerical modeling has been limited to pilot scales, ignoring the performance optimization required for scaling up the gasification process. Gasification is a highly complex process, which involves the coupling of thermochemical equilibrium, kinetics, heat and mass transfer, and computational fluid dynamics. This complexity has currently prevented the proposed theoretical/computational models in the literature from achieving the required accuracy for optimizing the gasification process. Herein, we offer a comprehensive guideline to improve the numerical models which can be implemented in future sustainable biorefineries to improve their efficiency. The present study pursues two principal objectives: (1) Introducing the fundamental knowledge required for theoretical/computational modeling and (2) Reviewing alternative numerical models for gasification process. First, a brief overview of the knowledge needed to make a systematic model is gathered. The theory of gasification, the various types of gasifiers and their differences are reviewed. Furthermore, we discuss the importance of the type of biomass feedstock with concentration on advanced biofuels and focus on wood pellets for the modeling section. Second, CFD is introduced and chemical equilibrium, kinetics, and heat and mass transfer models are discussed in depth and the variation of different parameters with respect to the change of temperature within a gasifier is elaborated. The results of this study make a clear pathway for modeling of gasification process by anticipating the expected outputs from the model by using the existing experimental data. Finally, comprehensive application of these models is demonstrated and substantial parameters affecting the gasification process are introduced. This paper provides a framework for numerical modeling of the gasification process of biomass to optimize the efficiency of the conversion process.