Food waste is a global challenge for the environment but also an available fuel with complex components. In this paper, rice, lettuce, and fish residue (contained meat and bone) were selected as typical components of daily food waste. The co-gasification reactivity of three food wastes with Shenfu coal was tested via thermogravimetric analysis. The interaction mechanism was further studied via scanning electron microscopy-energy-dispersive X-ray spectroscopy, heating stage microscope, and Fourier transform (FT)-Raman techniques. The lettuce/fish waste char presented great synergy with coal char during co-gasification, whereas no synergy was observed during co-gasification of rice char and coal char. During co-gasification of lettuce/fish waste char and coal char, the ash from lettuce (rich in potassium) and fish residue (rich in calcium) migrated to the surface of coal char and further catalyzed the coal char gasification. The synergetic effect was further confirmed via a high-temperature stage microscope. In addition, The FT-Raman analysis showed that the lettuce and fish ash increased the reacting sites of Shenfu char and inhibited the degree of graphitization.