The invention discloses a preparation method of a wood-plastic composite material aid. The aid is aluminum oxide-aluminum nitride composite heat-conducting ceramic composed of aluminum oxide heat-conducting ceramic and aluminum nitride heat-conducting ceramic. The preparation method mainly comprises the following steps: ball milling, calcination, ball milling, granulation, sintering, pulverization and the like. By adding the aluminum oxide-aluminum nitride composite heat-conducting ceramic, the wood-plastic composite material can have favorable mechanical properties and low water absorptivity, and thus, has wider application range and longer service life. Besides, the aluminum oxide-aluminum nitride composite heat-conducting ceramic has a certain porous structure, and thus, can adsorb harmful gas and purify air, thereby being beneficial to environmental protection. Therefore, the preparation method of the wood-plastic composite material aid has great development potential.