The invention discloses an outdoor polystyrene composite material. The outdoor polystyrene composite material comprises, by weight, 1000 to 2000 parts of recycled foamed plastic polystyrene, 50 to 300 parts of wood flour, 20 to 100 parts of an interfacial modifier, 1 to 30 parts of a foaming agent, 5 to 50 parts of a nucleating agent, 50 to 200 parts of white oil, 100 to 1000 parts of an impact modifier and 3 to 20 parts of an antioxidant. The invention also provides a preparation method of the outdoor polystyrene composite material. The outdoor polystyrene composite material has good mechanical properties and thermo-oxidative aging resistance and can be used for a wood plastic chamber inner door, a skirting line, an integrated cupboard, a wardrobe, an exterior wall cladding, a smallpox suspended ceiling, a decorative wall panel, an outdoor floor, a guardrail post, a plastic steel pavilion, a balcony guardrail, a field fence, a leisure bench, a tree pool, a pergola, a flower box air conditioner rack, an air conditioner conditioning shield, window-blinds, a road nameplate and a transport tray.