The invention relates to a wood plastic material and particularly relates to a micro-foaming wood plastic composite sheet and a preparation method thereof. The method provided by the invention comprises the following steps: evenly mixing polyvinyl chloride, nano-montmorillonite, calcium carbonate powder, white oil, a heat stabilizer and mica powder are uniformly stirred; and then carrying out extruding pelletization to obtain modified plastic particles; and then uniformly stirring the modified plastic particles with wood meal, azobisformamide, a foaming regulator, chlorinated polyethylene andan ultraviolent absorbent, and performing extrusion and foaming formation to obtain the micro-foaming wood plastic sheet. The micro-foaming wood plastic sheet has high degree of mechanization and lowcost, is lower in density, less in plastic amount and more environmentally-friendly compared with plastic sheets, is lower in density and higher in impact strength compared with other wood plastic materials, is lower in weight and cost and more convenient in installation and maintenance compared with gypsum boards, aluminum pinch plates and the like, and also has an air purification function. Themicro-foaming wood plastic sheet can be manufactured into products, such as photo frames, picture frames, skirtings, hangers and pinch plates and the like, and is widely applied to plenty of occasions, such as halls, guest houses, small offices and the like.