Alloys of different nominal composition Nb3(Al1-xGex) (where x = 0.20, 0.23, 0.25 containing A15 + σ phases) have been heat-treated under high pressure up to 67kbar. With increasing treating pressure, 1) the lattice parameter of A15 phase as well as the I211/I210 of relative integral intensity of X-ray diffraction peak (211) and (210) of A15 phase having some concern with structure composition both exhibits a maximum, 2) the structure composition of A15 phase shifts toward the Nb-rich direction, 3) the superconducting transition temperature Tc decreases, while the width of superconducting transition temperature range shows a maximum. The results were discussed.