The competing and reciprocal relation model of winter wheat root and shoot is described. The root and shoot equilibrium and growth stability is studied on the basis of kinetics system theory. Result assumes that root and shoot, as the whole functional structure of crop, having been pursuing mutual equilibrium in their life, but they can not come to a equilibrium state forever, they are always in a disequilibrium state from beginning to end of their life, this is the essence of root and shoot equilibrium. Here it is suggested that neither the root nor the shoot can develop no limit, they are all controlled by the growth behavior of crop. Water stress inhibit the function of root and shoot, minish the mutual influence of root and shoot, as a result, make the crop growth gradually tend to stebility. The stably growth time of crop become longer with water stress aggravating. Rewatering augment the mutual influence of root and shoot, promote the rate of dry matter acumulation (DMAR), prolong time of instable growth, as a result, crop show a extra-compensatory effect. Rewatering during flowering stage can upset the inherent relativity long time stable growth during flowering stage, lead to growth unstably, promote DMAR.
