Taking into account the saturable nonlineary of the optical fibers, the coulped nonlinear Schrdinger equations of the slowly varying envelopes for two optical waves of different frequencies with the same polarizations, and the linearized nonlinear Schrdinger equations for the perturbations are given. In the normal dispersion region of optical fibers, the variation law of the gain spectra of modulation instability induced by cross-phase modulation with the input powers of the two waves is analyzed and discussed. The results indicate that, similar to that of the gain spectra of self-phase modulation induced modulation instability in optical fibers with saturable nonlinearity, the critical perturbation frequency as well as the peak gain of cross-phase modulation induced modulation instability also increases with the input powers before decrease. The varying velocity of the two parameters is related to the perturbation frequencies. This may lead to a unique value of peak gain and critical perturbation frequency for two different input powers.