The emergence of cloud computing greatly changed the usage model of existing information technology. Its obvious efficiency of cost reducing will significantly cut down the information barrier, deepen integration of informatization and industrialization, thus bring in positive macroeconomic effect. However, little researches focus on this phenomenon. Therefore, this paper adoptes a dynamic stochastic general equilibrium(DSGE) model with the endogenous market structure to analyze the macroeconomic impacts of the application of cloud computing in small and medium size enterprises thanks to the characteristics of cloud computing of turn fixed costs in IT into variable cost. Based on the data of 2014, the results show that cloud computing technology diffusion will promoting our country's GDP growth of 0.42% ~0.79%, the employment rate increased by 0.06%~0.13% and the number of SMEs increased by 1.44%~2.82% after five years. In addition, we find that cloud computing has more influence on undeveloped area compared with developed area. Finally, several targeted recommendations and proposals are raised on cloud computing technology development according to above conclusions．