The dispersive transfer function has been derived in this paper to describe the distortions on pulse propagation in the ionosphere. As the crucial parameter in the function, the dispersive coefficient has been discussed and calculated on condition that the ionosphere is spherical stratified. Furthermore, simulation has been conducted to illustrate the low-pass filtering modulation and pulse mixing influence by convoluting with the dispersive transfer function. Eventually, two illustrative examples provide additional insight to explicate the ionospheric dispersive effect on Gaussian pulse and narrow band LFMCW signal.