The influence of the earth's curvature on calculation of ionosphere reflection coefficients at LF and VLF bands is discussed. By developping Maxwell equations in the spherical coordinate, a differential equation system for transverse components of electromagnetic waves has been achieved. The value of admittance matrix A at the bottom of ionosphere is able to be countted with the similar method given by Budden.Then the ionosphere reflection coefficients is able to be countted with the spherical stratified model.