The invention provides a preparation method of a flame-retardant epoxidized natural rubber composite material and relates to preparation methods of rubber composite materials. According to the preparation method, the surface of the traditional flame retardant ammonium polyphosphate (APP) is coated with dopamine by adopting an interface functionalization modifying method so as to form a dopamine film on the surface of the APP, interface bonding is achieved through interaction between the dopamine and epoxidized natural latex, and then, the flame retardant and epoxidized natural rubber are integrated. According to the preparation method, the flame retardant and a rubber matrix are combined by means of chemical bonding, and thus a cross-linked network structure is formed, so that the flame retardance and mechanical properties of rubber are greatly improved compared with the existing circumstances that the flame retardant and the matrix are only blended simply and mechanically.