Biomass energy is critical to future low-carbon economic development facing the challenge to mitigate the high carbon emission from conventional energy exploitation. Biomass energy developed from energy plants will play a more important role in future energy supply in China. As cultivated land resources are limited and critical to food security, the development of energy plants in China should rely on the exploitation of marginal land. In this study, based on three scenario-based (RCP2.6, RCP4.5 and RCP8.5) land cover datasets, the Net Primary Productivity (NPP) dataset, the dataset of marginal land suitable resources for cultivating bioenergy crops, and protected area dataset, firstly, we spatially identify and quantify the available areas of three types of marginal land, including abandoned agricultural land, low-productivity land and the ‘rest land’; then, the geographical potentials of biomass energy are calculated through multiplying the available area for energy plants by the corresponding productivity out to 2100 in China. The results show that significant potentials for biomass production are found in the south of China, such as Yunnan, Sichuan, Guizhou and Guangxi provinces. The total geographical potential biomass energy of the marginal land ranges from 17.813 to $$19.373\,\hbox {EJ}\,\hbox {year}^{-1}$$ under the three scenarios, reaching the highest under RCP8.5 scenario, and the geographical potential biomass energy of the ‘rest land’ is the largest contributor, accounting for more than 90% of the total potential biomass production.