The morphological structure of avian digestive system is closely related to the energy intake.This essay takes the tree sparrows with full food-intake in the same environment to be the control group and compares it with four groups of Tree Sparrows (Passer montanus) that are in same conditions and at different time of starvation(1,3,5,7 day)in terms of the length and weight of digestive organs.The results showed that the body weight and body fat were decreased in four groups acclimation birds,the length and weight of digestive organs were increased obviously in P.monanus of one day starvated,the tracts showed increase-decrease-increase pattern in four team birds of hunger days add,food-intake and stomach dry weight was significantly correlated.The conclusion is that different requirements for food-intake result in the great changes in the length and weight of avian digestive organs and the changes involve such aspects as the length,the capacity and the biological structure.These changes may have direct effects on the food-intake and the digestibility.Meanwhile,this kind of adaptive change should be fast,reversible and repeatable.It is the result of energy budget between the morphological structure and function and the energy expenditure of the organs themselves and also between the individual and environmental and fitness.