A natural in-situ extraction was conducted to study the effects of exudates and returning residue to field from sesbania (Sesbania cannabina) on growth of Bidens pilosa, Echinochloa crusgalli, Raphanus sativus and soil environment in order to evaluate the ecological effects of sesbania cultivated as green manure. The results showed that natural in-situ exudates and returning residue of sesbania inhibited plant growth, especially in Echinochloa crusgalli, while increasing significantly of soil microbial biomass and enzyme activities, and these positive influences were confirmed by field survey, which indicates that planting sesbania as green manure is feasible.