In order to study the load reduction effect of expanded polystyrene (EPS) foam board of Marston effect in high fill culvert, the principle of load reduction of polystyrene foam board and the limitation of current improvement are analyzed by utilizing the theory of elastoplastic mechanics, soil arching effect and the form of Marston effect. Based on the principle of the load reduction effect of expanded polystyrene foam board, the ABAQUS model was used to establish the load reduction model of expanded polystyrene foam with different laying heights. The optimal expanded polystyrene foam laying height is obtained by the comparison and analysis of the calculated results. The results can provide guidance for practical engineering application.