There are many advantages and extensive application prospect in applying optical fiber technology to free space laser communication system.Unfortunately,it is difficult to coupled spatial light to fiber.And then the coupling efficiency is the key of the application.In this paper,we simulated the effect of atmosphere turbulent on the facula shape,and measured the facula with CCD,analyzed the characteristics of facula,such as the energy distribution and the size of the facula,especially when the maximum light power in the centre of the facula is beyond the range of CCD.Based on the distribution what we had got previously,we calculated the light power in the centre of the facula.Then we could fit the energy distribution actually,and then we can get the radius of the facula.The research of the facula′s characteristics is very essential.It offers the theoretic foundation for choosing the adequate fiber core′s diameter and numerical aperture（NA）.And it can also be used to estimate the coupling efficiency of spatial light to fiber.