This paper presents a new technique for flat optical frequency comb (OFC) generation, which is based on the nonlinear process of multiple four-wave mixing (FWM) effects. The nonlinear effects are significantly enhanced by using the proposed optical feedback scheme consisting of a single mode fiber (SMF), two highly nonlinear fibers (HNLFs) with different zero dispersion wavelengths (ZDWs) and polarization beam splitters (PBSs). Simulation results illustrate its efficiency and applicability of expanding a comb to 128 coherent lines spaced by only 20 GHz within 6-dB power deviation.