The effects of signal spatial coherent characteristics and receiving aperture size on normalized carrier-to-noise ratio (RnCN) and field of view for coherent detection (Ωf) are investigated. In the model of remote laser radar detection, the expressions of RnCN and the receiving theory are presented. Further numerical simulations show that when the Gaussian local oscillation beam size is larger than the receiving aperture size, RnCN will reach saturation, in addition, the spatial coherent length and aperture radius can both improve RnCN, but will reduce Ωf. Based on the theoretical analysis and numerical simulation, the relation is presented that the product of RnCN and field of view is proportional to λ2, which is unaffected by the coherent characteristics. At last, the dependence of RnCN on the detection height and ground range under the turbulence model of Hufnagel-Valley 5/7 is analyzed.