Abstract: Scope economy is a goal pursued by enterprises, and the expansion of a company's scale, under certain condition, is a tool used by entrepreneurs for the realization of a company's scale economy. Whereas scope economy is not to be equated with a large scale, it usually indicates a moderate and effective size. Small and medium sized enterprises are characteristic of a small scale, a small amount of investment, and flexible management, which compared with large scale enterprises can be disadvantages in marketing condition, such as labour force, technique, capital, and information, etc. Thereby in the scale expansion, the development scale of small and medium enterprises should not be just as big as possible, it should be within the extension of scope economy, and should be determined by different periods of lifecycle, which is rational choice for prolonging lifecycle.