<p>The third-generation bioenergy crops as microalgae have a wide range of advantages, including high growth rate, high oil content, and low land occupation. In particular, their placement on abandoned croplands will not compete for croplands with food production. However, the bioenergy potential of microalgae on abandoned croplands is still unclear. In this paper, we identified abandoned cropland in China from 2000 to 2020. On this basis, we estimated the bioenergy potential of microalgae on abandoned cropland by conducting historical and scenario experiments. The results showed total abandoned croplands reached about 29.75 million ha in China from 2000 to 2020, and the abandonment rate was 11.07%. In addition, the projection indicates that the potential production of microalgal bioenergy on such abandoned croplands is to increase in different SSP-RCP (shared socioeconomic pathway-representative concentration pathway) scenarios in future decades. It can offset 8.26 × 10⁹ GJ year⁻¹, about 22.83% of carbon emission from fossil energy consumption in China in 2020. The average annual production of bioenergy from microalgae in the historical period accounts for 4.76% of the global oil consumption in 2020. The bioenergy potential of microalgae is about 8.8 and 1.2 times higher than that of the first- and second-generation bioenergy, respectively. Spatially, microalgal bioenergy production is significantly higher in the south-western and south-central China than in the other regions. The phenomenon can be attributed to the differences in elevation, NDVI (normalized difference vegetation index), and sunshine duration. Furthermore, their interactions among these factors were significantly stronger than the effects of any single one. The findings provide a guidance to the effective utilization of abandoned cropland and bioenergy deployment at large scales.</p>