The invention discloses a micro-foaming polyethylene-matrix wood-plastic composite material and a preparation method thereof. The micro-foaming polyethylene-matrix wood-plastic composite material is prepared by the following steps of stirring a matrix polyethylene resin, modified wollastonite powder and talcum powder, a crosslinking agent, a lubricant, a heat balance type foaming agent, an antioxidant, an anti-ultraviolet agent, pigment and modified plant fiber, heating and uniformly mixing, then cooling and discharging to obtain a premix, wherein the modified plant fiber is one of wood powder, bamboo powder and rice hull powder or a mixture of two or more at any proportion; putting the premix into an extruder, and performing granulation, extrusion foaming and cooling formation. The micro-foaming polyethylene-matrix wood-plastic composite material disclosed by the invention is convenient to produce and manufacture, the raw materials are cheap and environment-friendly, the average diameter of the pores of the micro-foaming polyethylene-matrix wood-plastic composite material is reduced to 10 microns, and the content of the plant fiber is increased to 45%; moreover, the composite material has low density and high bending strength and impact toughness, is widely applicable and can be applied to the fields such as decoration, building, municipal administration, packaging, automotive upholsteries and the like.