The invention provides a degradable flame-retardant wood-plastic composite and a preparation method thereof. The wood-plastic composite material is prepared from the components of waste polypropylene, waste low-density polyethylene, nanometer kaolin, polyhydroxybutyrate, poly(ethylene naphthalate), modified berberis amurensis powder, shell powder, glass fiber, quartz fiber, bronyl acetate, itaconic acid, disodium maleate, ethylene bisstearamide, composite flame retardant, coupling agent and stabilizer. The degradable flame-retardant wood-plastic composite material is degradable, impact strength of the composite material is up to 9.3-10.7kJ / m<2>, the tensile strength is up to 43-55MPa, the flame retardant rating is up to grade UL-94 V0, the formaldehyde release amount is 0.036-0.071mg / L, and the standard of less than 1mg / L of formaldehyde release amount of materials used in interior architecture environments is met.