To achieve energy transformation and reduce carbon emissions, renewable energy must be developed vigorously. As an important part, biomass energy can be used in a variety of ways and has good prospect for development. Biomass gasification-coal coupling for power generation is an important technology and development direction of biomass energy utilization, which has a small impact on the coal-fired boiler, high power generation efficiency and is easy to monitor electricity. In order to investigate the system characteristics of biomass gasification-coal coupling for power generation, it is first necessary to understand the biomass gasification process and obtain the components of biomass gasification gas and related gasification indexes. This paper establishes a biomass gasification model based on thermochemical equilibrium, and obtains the relationship curves between gas components, gasification index and gasifying agent equivalent ratio, water content through Visual Basic programming. The results show that with the increase of water content, the calorific value of gas and the gasification efficiency decrease, whereas the gas production rate increases. And as the gasifying agent equivalent ratio increases, the gas production rate and gasification efficiency increase, while the gas calorific value decreases. These relationship curves can provide reference for the gasification process control, and can also lay the foundation for the design and optimization of the biomass gasification-coal coupling for power generation system.