The invention discloses an environment-friendly and low-cost filling material suitable for a goaf in tunnel construction. The environment-friendly and low-cost filling material comprises the followingcomponents: gangue, papermaking causticized white sludge , sodium polyacrylate, modified graphene oxide, sodium bentonite, a foaming agent, a foam stabilizer, a water reducing agent, coal ash and water. All the main raw materials of the environment-friendly and low-cost filling material are industrial wastes harmful to the environment and are not only low in cost, but also remarkable in environment governance effect; a small deal of nitrogen-doped graphene oxide is added in a hydrogel form, and modified graphene coats the periphery of the sodium bentonite due to a specific stereostructure, sothat the sodium bentonite is capable of keeping structural stability and has an impact-resistant effect after expanding by absorbing water in a preparation process, in addition, the compression strength of the finally prepared filling material is twice or above higher than that of the filling material in which traditional sodium bentonite is added.