Based on the generalized Huygens-Fresnel principle and the modified Von Karmon spectrum mode, the analytic expression of mean intensity of partially coherent Gaussian- Schell model (GSM) beam, which is propagating in the atmospheric turbulence along an uplink path, is derived. The analytical formula of mean intensity of GSM beam which is echoed through corner reflector and propagated along a downlink path to the receiver is obtained and normalized. The change of mean intensity of GSM beam when it is propagating along an uplink and a downlink path is analyzed, in the case that the transmitter and the receiver are located on the same height. The results of numerical analysis show that the influence of turbulence to collimated beam is smaller than it is to focused beam, when they propagate along a double slant path in the atmospheric turbulence. On the receiver, with the increase of corner reflector radius, the axial normalized intensity first increases, and eventually tends to be constant. The axial normalized intensity decreases with the increase of turbulence inner-scale, but nearly has no change with the increase of turbulence outer-scale.