From creation to the bankrupt of company, it will experience a series of intermediate stages of development. Growth stage is the key one during the process of enterprise’s changing rapidly. With the characters of business growth stage, this pa rise’s changing from weak to strong. In this stage, enterprise rises quickly whose influencing factors are per brings in entropy theory. Based on size, complexity, stability of enterprise, the paper establishes a kind of model of measuring and calculating business management entropy around business size, enterprise capacity and developing speed. The model will supply theoretical direction for decision making activities of business growth stage.