The paper presents the results of modeling ionospheric parameters using the Global Self-Consistent Model of the Thermosphere, Ionosphere, and Protonosphere (GSM TIP) of the Earth. Numerical experiments have been performed for three variants of the solar EUV spectrum data: the Nusinov model, EUVAC, and generalized solar flux measurements (SOLID). The calculations have been carried out on March 22, 2009 (F-10.7 similar to 68) and March 22, 2014 (F-10.7 similar to 154). The maximum ionization rate and, correspondingly, the critical frequency of the F2 layer have been obtained using the Nusinov model for low and high solar activities. The lowest ionization rates and values of foF2 have been obtained using the EUVAC model. Simulations with the SOLID spectrum show the better agreement of foF2 with the empirical model IRI-2007 at the maximum solar activity. At the same time, at the minimum solar activity, all models of the spectrum provide an underestimation of the values of the critical frequency of the F2 layer.