The ternary GdFeSi compound doped with Ti or Al as the GdFe1-xTixSi and GdFeSixAl1-x series is investigated theoretically and experimentally in this work. The parent and Ti doped compounds are found to crystallize into the tetragonal structure, in the Al doped compounds, the cubic and hexagonal phases are also found in addition to the original tetragonal phase. GdFeSi is interesting for the presence of a magnetocaloric effect with a maximum -ΔSM(T) value of 5.0 J/kgK. With increasing Ti content, the Curie temperature TC is found to increase quickly for x = 0-0.1 and then, more moderate change is observed, similar to the Al doping. The electronic structure and magnetic moments for GdFe1-xTixSi and GdFeSixAl1-x are calculated theoretically within DFT+U taking into account strong electron correlations in 4f Gd shell. The calculated electronic structure demonstrates a significant increase of the density of electron states at the Fermi level for some compositions which accompanied by the rapid growth of TC in the GdFe1-xTixSi system.