Background: All-optical processing has a huge superiority in speed and efficiency than traditional optical-electrical-optical signal processing. Four-wave-mixing is an important nonlinear parametric process to achieve all-optical processing.Objective: We proposed the photonic crystal waveguide to enhance the conversion efficiency of four-wave-mixing significantly in practical application. Methods: We demonstrated a waveguide composed of silicon with mono-layer graphene-coated as core and Si-Ge distributed periodically on both sides as cladding. By the introduction of the slow light effect of Si-Ge photonic crystal and the localization effect of graphene, the conversion efficiency of four-wave-mixing had enhanced dramatically. Results: The conversion efficiency can be increased by 16dB compared with a silicon waveguide. The maximum efficiency as high as -9.1dB can be achieved in the Si-Ge-Graphene photonic crystal waveguide (SGG-PhCWG). The propagation loss can be decreased to 0.032dB/cm. Conclusion: Numerical results of the proposed SGG-PhCWG matched well with nonlinear coupled- mode theory. This configuration offered a new physical mechanism and solution for alloptical signal processing and high-efficiency nonlinear nanoscale devices.