Abstract: Amplitude scintillation affects adaptive optics correction seriously when laser propagates long distances nearly horizontally in atmosphere. Field correction can be fulfilled with two-deformable-mirror adaptive optics. The result of correction is affected by the choice of beacon wavelength. Expressions of field variance and beacon wavelength for phase and field compensations are derived by Rytov approximation. The calculated results show that when the ratio of beacon wavelength to main laser wavelength is less than 1.89, field variance of full field compensation is less than that of phase compensation.