Abstract: The fluctuations of PV power output is a significant factor that affects the development of PV power generation. In this paper, the fluctuation characteristics of PV power output in different time scales is studied through statistical calculating and analyzing of historical operation data of a PV power plant. The impact of the output fluctuations of grid connected PV power generation on power grid is discussed briefly, and the fluctuation level of the PV power output is analyzed quantitatively. Then the fluctuation data of PV generation output in different time scales show fitted with probability density of 3 kinds of distribution functions, and the results show that the fluctuation characteristics of PV generation output in different time scales should be described by choosing different distribution models of probability density.