In this paper, the propagation properties of the Laguerre-Gaussian (LG) beam passing through Cassegrain antenna system in a turbulent atmosphere have been researched. The accurate analytical function for the diffraction field of LG beam passing through Cassegrain antenna, the average intensity, and the cross-talk among different orbital angular momentum (OAM) modes of LG beam passing through Cassegrain antenna in Kolmogorov turbulent have been derived. The simulation results show that LG beam with ring-like distribution is selected to enhance the emission efficiency of Cassegrain antenna. The cross-talk among different OAM modes can remarkably reduce through using Cassegrain antenna. The analysis process can also apply to accurately analyzing the propagation properties of other kinds of beams through different optical systems in turbulent atmosphere.