Life cycle assessment analysis method was used to establish the life- cycle energy consumption and emission inventory, and evaluate the environmental impacts of bioethanol production produced from sweet potato with two different fertilization modes, that is, conventional fertilization mode and soil testing & formulating fertilization mode. The sweet potato based ethanol production system was divided into three subsystems, including crop cultivation, feedstock transport and ethanol conversion. The energy consumption and pollutant emission inventory of sweet potato based ethanol was established with the unit of 1 000 L ethanol production. The results show that the energy efficiencies of the two sweet potato based ethanol production systems were 1.41 and 1.43. The main environmental impacts of ethanol produced from sweet potato with conventional fertilization practice are human toxicity, eutrophication, acidification, freshwater ecotoxicity, energy depletion and global warming, their environmental impact potentials accounting for 40%, 40%, 31%, 29%, 25% and 20% of relevant environmental potential per capita in 2000. The soil test & formulating fertilization practice reduced the usage of chemical nitrogen and phosphate fertilizers and increased the fertilizer utilization efficiency and sweet potato yielding, so the environmental impact indexes of eutrophication, freshwater ecotoxicity, acidification and global warming were decreased by 31%, 15%, 9% and 7%, respectively. Therefore, soil testing & formulating fertilization mode can improve life-cycle energy efficiency of the sweet potato based bioethanol and significantly alleviate its negative environmental impacts.