Substituting fossil fuels with bioenergy is one of the most promising options for energy transition in China, and abundant forest biomass plays an important role in this process. In this study, the mitigation effects and economic benefits from substituting wood pellets for coal in heat and power generation in China were investigated, based on a life-cycle assessment and economic contribution analysis using the system boundaries defined for the two energy systems in terms of greenhouse gas emissions and economic cost. The results suggest that: (1) When wood-based pellet replaces coal in heat and power generation, the life cycle energy consumption per unit of energy produced decreases (0.01-0.176 MJ), and the greenhouse gas emissions are significantly reduced if wood pellets are assumed to be carbon neutral; (2) Based on the average market prices of wood pellets and coal, the cost per unit heat or electricity generation by burning wood pellets is higher than that of coal (16.06-34.16 Yuan), because the energy used in wood pellets production is more costly; (3) The sensitivity analysis suggests that energy conversion efficiency, fuel energy content, and fuel price are the most important factors that affect the effectiveness of energy substitution; and reducing energy consumption and the overall cost for producing wood pellets is most effective for reducing the substitution cost and creating a win-win situation for both climate mitigation and economic development. The development and utilization of forest biomass play an important role in China’s energy structure transformation. This study can inform policy development from the aspects of emission reduction under carbon neutrality assumption, source of biomass, emission reduction efficiency, and financial subsidies.