Based on the generalized Huygens-Fresnel principle and the rough surface scattering theory, the effect of atmospheric turbulence on both pulse beam propagating to the target and scattering field propagating back to the receiver is studied, and the second-order statistical properties of pulses scattered by diffuse targets are investigated. An expression is deduced for the multiple-frequency mutual coherence function (MCF) of a reflected pulse beam from the rough target in atmospheric turbulence. According to MCF an expression of the mean intensity and the degree of complex coherence at the receiver is derived. The numerical simulation results indicate that the mean intensity is independent on the atmospheric turbulence, and the coherence bandwidth depends on the turbulence strength, the central angular frequency, the outer scale of turbulence, the position separation and the angular frequency difference when the phase structure function is dominant.