The invention provides a fiber-reinforced composite plate, as well as a preparation method and application thereof. The composite plate comprises a working layer and a reinforcing layer composited on the working layer, wherein the working layer is prepared from a chopped fiber reinforced polyurethane foaming material ; the reinforcing layer is prepared from a continuous fiber reinforced resin composite material. The fiber-reinforced composite plate provided by the invention can serve as a railway flatcar floor and has proper nail-holding power, good friction coefficient, high flame retardance and excellent mechanical stability, weather resistance and corrosion resistance ; the service life can reach 10 years or longer. The bearing capacity, the deformation, the connecting bolt tightness degree and the surface condition after the railway flatcar floor is ground by tracks repeatedly of the railway flatcar floor manufactured by the fiber-reinforced composite plate provided by the invention are obviously superior to those of the wood floor.