The invention relates to a foaming plastic wood composite material board and a preparation method thereof. The preparation method comprises the following steps: processing wood powder by using an aluminic ester coupling agent to obtain coupling agent modified wood powder; evenly stirring the coupling agent modified wood powder, plastic particles, alkali magnesium sulfate whisker and lead sulfate tribasic, extruding and pelleting to obtain composite material particles; evenly stirring the composite material particles, azodicarbonamide, composite foaming agent, terpene resin, ethylene bis stearamido and light stabilizer, and extruding to prepare the foaming plastic wood composite material board. The invention has the advantages of convenient production, low production cost, small use amount of plastics, environment friendliness, no aging or discoloration, no buckling deformation, low density, light weight and high impact strength, and has the function of adsorbing gas. The foaming plastic wood composite material board can be widely applied to households, office buildings and other buildings, can be manufactured to photo frames, picture frames, skirting and suspension plates, or can be used for manufacturing suspension cross beams, pergolas, and the like.