In recent years, global environmental problems such as air pollution and the greenhouse effect have become more and more serious. The utilization of biomass energy not only can promote low-carbon transformation to establish a competitive advantage through value creation under the goals of carbon peaking and carbon neutrality but is also an important force in solving environmental problems. Government subsidy policies play an important role in promoting the development of biomass energy utilization. Taking straw as an example, this paper constructs a straw recycling supply chain system dynamics model consisting of farmers, acquisition stations, power plants, and pyrolysis plants based on a real-world case. Two types of straw processing, namely power generation and pyrolysis, are considered in the model. This paper analyzes the economic and environmental impacts of three subsidy policies, namely the unified rate policy, the linear growth policy, and a two-step policy, by comparing the profit, carbon, and pollution emission reduction benefits of the supply chain under different subsidy scenarios. The result shows that, among the three subsidy policies, the unified rate policy shows the best-promoting effect. The research results and policy implications in this paper could be a reference for governments trying to formulate subsidy policies for developing biomass energy utilization.