Abstract: Under film covers of wheat, the variatioa treads of CO₂ concentration are similar despite of different sowing time, old or new plastic films, or sunny or cloudy days. The diurnal course of CO₂ concentration can be divided into 3 stages: gradual rise, straight line drop and cyramic equilibrium. There will be lack of CO₂ in varying degrees when it is below the(ynamic equilibrium. Increasing CO₂ concentration under plastic films will greaty promote the photosynthesis and yield of late owing wheat.

Key words: grassland grasshopper plague, climatic suitability, habitat suitability, fuzzy evaluation, 3S technology, integrated evaluation model