Several parameters influence anaerobic digestion, e.g., hydraulic retention time, temperature, pH, pressure, C/N ratio, etc. This work presents the influence of the C/N ratio of the substrate on biogas production modeling. To do this, a mathematical model is developed for predicting the molar composition of biogas as a function of the C/N ratio. Inspired by the AM2HN model, this model is a system of nine partial differential equations that have been solved numerically in SCILAB software by the 4th-order Runge-Kutta method. Obtained results show an increase in production of methane with the C/N ratio. Thus, optimal production of methane is observed for a C/N value between 20 and 30. The proposed model is then tested with two other models; these tests show that the results of the proposed model match well with numerical results of those two models.