Abstract: According to the concrete conditions in southern Jiangsu,the significance,necessity and possibility of ad-justing cropping structure are evaluated from the viewpoints of niche theory.The efficiencies of two crop-ping systems in utilizing paddy field niches are analyzed and the results show that the cropping pattern ofwheat intercropped with lettuce,followed by corn and late rice is an effective model to improve niche functions in the district.

Key words: Qinghai-Tibet Plateau, UV-B radiation, Vicia angustifolia, biomass, flowering phenology, seed yield.