The modified Rytov theory was applied to study the Laser beam propagating through the atmospheric turbulence under the double slant path. According to the Born approximation and the kolmogorov atmosphere turbulence power spectrum, the general expression of the optical scintillation both on target's plane and on receiver's were given, and further based on the atmospheric structure constant of ITU-R, the characteristic of the optical scintillation index was analyzed with different parameters altitude. The study showed that the characteristic of optical scintillation index on the target's plane and the receiver's have a nearly connection with the characteristic of scattering field except the altitude effect and so on.
