Abstract: Using the random medium wave propagation theory, we studied the characteristics of signal fluctuation in the rainfall scattering environment, and the effects on the multipath channel due to (multiinput multioutput，MIMO) channel correlation of satellite communications. We also deduced the formula for calculating the correlation coefficient between the receiving antennas and transmitting antennas in the rainfall environments. Then， we discussed the correlation coefficient advanced. The results show that the distance between antennas, the frequency, the rainfall rate and other factors have an important impact on the correlation coefficient of MIMO system for satellite communications.