Abstract: Scintillation increases when laser propagates long distance near horizontally in the atmosphere, which limits the ability of conventional adaptive optical system. Numerical simulations based on wave optics computer code are given for different atmospheric conditions. For given Rytov variance, different turbulence strengths and propagating distances are considered. Various receiving and projecting apertures are also taken into account. Rytov variance and propagation Fresnel number have still effect on Strehl ratio. The expressions of Strehl ratio with Rytov variance are obtained from weak to strong scintillation. For given Rytov variance, Strehl ratio with Fresnel number is studied. Large aperture can benefit correction. The results show that Strehl ratio increases with Fresnel number incre