The article presents a new approach to forecasting the composition of producer gas. Thermochemical treatment of biomass as an effective method of producing flammable gas was presented. The methods of predicting the gas composition of the generator are described, and then its efficiency depending on the parameters of the device. In order to create a method for forecasting gas composition, the authors' works were used as the basis, in which the energy characteristics of the gases obtained were assessed. It was assumed in this paper that it is very important to understand the influence of each parameter on the energy characteristics of the gas. This made it possible to optimize the composition and predict thermal characteristics. In this article, we present the results of experimental studies on biomass gasification and a mathematical model based on Gibbs free energy.