Visibility is a crucial factor of affecting link performance in free space optical (FSO) communication. The bit-error rate (BER) model which does not consider the effect of turbulence is built. On this basis, the affect of receiving aperture on BER under different visibilities is studied by combing the actual visibility data and using the method of simulation. The results show that there are many differences between receiving aperture and BER under different visibilities. If the visibility is high, the BER is much lower, and the performance of system is better. The improvement of the receiving aperture on BER is obvious. At the same time, combining the requirement for BER in engineering practice, the choice of appropriate receiving aperture is discussed under different visibilities, which provides valuable theoretical reference for building the FSO communication link.