We investigate highly efficient frequency-degenerate parametric generation through inverse four-wave-mixing (IFWM) in silicon nanowaveguides, which exhibits distinctly from traditional FWM phenomenon and manifests itself as a unique process producing signal and idler photon pairs with frequencies at the center of two pumps. The influences of dispersion, nonlinear coefficient and frequency detuning on the IFWM process are numerically analyzed in detail. On this basis, the optimal condition for high gain IFWM and the nanowaveguide with high nonlinearity and large normal dispersion are proposed. These results substantiate the feasibility of such frequency-degenerate parametric generation in CMOS-compatible integrated platforms, which could find important potential in signal-processing systems for photonics networks and entangled qubits generation for quantum optics.