The present paper deals with the effect of short-term continuing food restriction on Tree Sparrows’ (Passer montanus) body weight and BMR (basal metabolic rate) as well as their physiological adjusting mechanism. The Tree Sparrows fed regularly were selected to be the control group (0D,D for day) and four groups of sparrows with same food-intake but different hunger hours (1D,3D,5D and 7D) to be the objects of study and acclimation. The results shows that there exists marked linear relationship between the body weight and BMR (r=0.512,P=0.001). There is no distinct difference as for the BMR level of unit weight among the five groups of Tree Sparrows,but distinct between the 5D and 7D team of body’s BMR(P<0.05). Tree Sparrows of the control group gain weight,while sparrows of the four acclimation groups lose weight on different levels. Compared with the control group,the degrees of weight loss for the sparrows of experimental group 1D and 7D become respectively marked (P<0.05) and extramarked (P<0.01); sparrows of group 3D and 5D have weight down,but still show slight increase compared with group 1D and 7D. The continuous starvation of 1 to 7 days causes the sparrows’ weight to present a down-up-down changing tendency. The conclusion is that when food-intake is not sufficient,consuming the body’s energy reserves and improving the digestibility are key points for sparrows to deal with the hungry environment and also one of their successful survival strategies.