Abstract: To study the law of body weight change of Glucocorticoid rats ,The Grey model GM （1, 1） was used to analyze and forecast the change of the rats body weight. The foreccust precision of GM （1,1） was high for the bodyweight change and the results were reliable，so the GM（1,1） could be used to forecast the bodyweight change of Glucocorticoid rats.

Key words: Glucocorticoid , Prednisone, Body weight , Grey model , Rat