Based on the modulation model of the power spectrum of refractive index fluctuation that includes the outer-and inner-scale, the effect of the finite outer-scale of the atmospheric turbulence on Fried coherence parameter is studied and a modified Fried parameter is developed. Results clearly show that atmospheric transverse coherence diameter is increased when the finite outer-scale of the atmospheric turbulence is considered, and the effect of inner-scale on atmospheric transverse coherence diameter can be ignored, because of the action between the atmosphere-turbulence lenses with the diameter (turbulent out-scale) and the Fried coherent lenses with the diameter Fried parameter.