In this paper, both a numerical model and an experimental study were developed to determine the important parameters of corn length for combustion behavior in a fixed-bed reactor. As an important factor impacting thermal conversion, changes in the burning rate follow variations in corn length, which then affect gas emissions. As a result of insufficient knowledge concerning the mechanisms of complex combustion, the development of a combustion system has been restricted. Modeling of this combustion system will complement experimental data; however, improving such a model is challenging as a result of the unique characteristics of corn, such as its moisture content and porosity. The results show that corn straw with a shorter length has a shorter ignition time, increased bed temperature, and reduced amounts of unburned carbon in the ash residues. Furthermore, the burning of shorter corn straw causes high emission concentrations from pyrolysis products, such as CH4, CO, and most prevalently NO, near the grate, which indicates the beginning of the char oxidation stage. Corn straw with longer lengths increases the difficulty of accurately modeling the irregular shape of corn straw particles for theoretical calculations. In addition, in an actual bed, local bed structures that have not been uniformly mixed result in uncertainties in the flame propagation as well as the time at which the fuel is ignited. The application of numerical modeling allows for a more detailed description of the corn combustion process and can be used as a reference to develop biomass combustion in a large system.