The (Fe40Ni40SixByCu1)(0.97)Nb-0.03 (Si/B = 3:1, 2:1, 1:1, 1:2 and 1:3) alloys were fabricated through the melt-spun technique. The effects of Si/B ratio on the glass-forming ability (GFA), phase transitions and soft magnetic properties were investigated. Results showed that when Si/B = 1:1, 1:2 and 1:3, the GFA of the FeNiSiBCuNb alloy is good, and the amorphous structure is homogeneous. We found a phase transition from the amorphous phase to alpha-Fe (Si) phase and then to gamma-(Fe,Ni)Si phase in Si/B = 1:1 alloy by employing a simple heat treatment process. The alloys with Si/B = 1:1 and 1:2 containing a low coercivity of 0.30 A/m and 0.25 A/m domain structures were characterized with magneto-optical Kerr microscope (MOKE) to unveil that the internal stress relief is beneficial to the magnetization process. The three alloys exhibit different crystallization behaviors, and moderate Si can effectively inhibit gamma-(FeNi) grains overgrowth.