A range of shortwave frequencies will be returned to earth by the ionosphere such that long-distance shortwave communication is accomplished. Because of ionospheric variations, operation parameters are not the same in different time duration. We must select optimized parameters with the aim of utilizing the ionosphere effectively for shortwave radio communications. Shortwave propagation prediction programs can provide such information. Empirical models are often used to represent the variations of the electron density with height in the ionosphere, since radio propagations are concerned with electron density. We develop a graphical user interface based on VOACAP that is one of the most widely used prediction programs. We also improve the electron density model in VOACAP. A gradient discontinuity occurs in the original parabolic ionospheric model. We incorporate an electron density model that does not contain any gradient discontinuities. In this model the electron density profile is composed of three segments: (1) a cosine F2 layer; (2) an E-F layer comprising a secant function, and optional cosine function to provide an F1 ledge (3) a parabolic E layer. Compared with experimental data, our modified model results in more accurate predictions.