The GdFeAl compound contains 42.8 wt% of the cubic phase of the MgCu2 (Fd3m)-type and 57.2 wt% of the hexagonal phase of the MgZn2 (P63/mmc)-type, the GdFeSi compound is a tetragonal of the CeFeSi (P4/nmm)-type phase, the GdCrAl and GdVAl compounds do not exist. In the GdFeAl1-xSix, GdFe1-xCrxAl and GdFe1-xVxAl substitutional compounds, the content of the cubic phase sharply increases and amounts to 62.3%, 99% and 99%, respectively, for the composition x = 0.2. The Curie temperature ТС(х) increases for the hexagonal and cubic phases in GdFeAl1-xSix, while for the tetragonal phase it decreases with increasing x. These various changes of ТС(х) are uniformly explained by the corresponding various changes of the density of states at the Fermi level N(EF) in the model of exchange interaction between the R and 3d ions in R-3d intermetallics, in which Tc ∼ N(EF). Ab initio calculations of N(EF) for the cubic, hexagonal and tetragonal phases in the GdFeAl1-xSix compounds have been carried out. The ТС(х) decreases in the GdFe1-xCrxAl and GdFe1-xVxAl systems for the hexagonal and cubic phases with increasing x. The saturation magnetization increases in the GdFeAl1-xSix, GdFe1-xCrxAl and GdFe1-xVxAl systems as x increases.