Abstract: Based on the Huygens-Fresnel integral and Rytov’s phase structure function, we formulated the average intensity and signal-to-noise ratio of a direction-detection imaging system in turbulent media. This paper presents the average intensity and signal-to-noise ratio (SNR) of diffused target scattering wave through turbulent atmosphere. The analytical expressions show the dependence of the average intensity and SNR on imaging lens, the turbulence strength and the object size. If the target size and lens size increase, or turbulent atmosphere decreases, signal-to-noise will increase.