As the basic force to promote the national economic growth and social stability, small and medium-sized enterprise is the most active economic subject in the market. Compared with the large enterprise, it has its distinctive characteristics. From the perspective of the dynamic evolution, this paper selects three dimensions of body mass scale, life cycle and elements demand to discuss the characteristics of small and medium-sized enterprise. The conclusion shows that: the body mass scale characteristics reflect in between individual and group and economic sectors; life cycle characteristics embodied in death trap and the change of spatial pattern; elements demand characteristics make timely adjust according to the stage of innovation content.