We have measured the saturated polar Kerr rotation of In-substituted single crystal BCVIG, Bi3-2xCa2xFc2-yIny (Fe(3x)Vx)O12, in the spectra range of 0.45-0.80 μm. A rotation peak near 0.47 μm was found. The room temperature dependence of the rotation peak value 2θK(0.47μm) on the composition was obtained by varying the substitution quantity of In3+ and Bi3+. It was found that the Kerr rotation change sign abruptly when varying the composition across the magnetization compensation point, however, the absolute value of the rotation does not reduce when the composition approaches that point, while the total magnetization 4πMs, does decrease, we also found that, with the In3+ content increasing, the Kerr rotation is "enhanced" at first, reaching a maximum at y～0.15, and then reduces. Using a model that the total Kerr rotation is the Bi3+ enhanced superposition of the sublattice Kerr rotation, we explained the "enhancement" of Kerr rotation by indium substitution. From fitting the experiment results, we deduced the ratio of the sublattice rotation coefficients (α4/α8) to be about 1.5, that is, the absolute contribution of every Fe3+ on tetrahedral site to the magneto-optic rotation is about 1.5 times as large as that on octahedral site. The results demonstrated that a good magneto-optic material can be synthesized in x3+ substitution. Considering its low and variable magnetization, high Curie temperature and rather large magneto-optic rotation, the In-BCVIG system, surely, is a promising cadidate in the variety of usage of the magneto-optic devices.