Abstract: Through fixed-plot experiments,effects of water stress in different growth periods on summer maize physiological and ecological process have been studied.The results show that the susceptibility factors for water stress in different periods to yield and its components are different.Soil water stress firstly acts on crop leaves and makes their water potential decrease,then leaves growth,photosynthesis and the transpiration of photosynthetic matters also decrease together.In the suitable situation of water stress,crop growth has a overshoot mechanism and stalk-mulching can relax water stress,at the same time have promoting influence on this overshoot mechanism.This mechanism should be applied to rain-fed agriculture or water-saving agriculture.