The invention discloses a mouldproof and inflaming retarding composite wood modifier, comprising a chitosan silver complex and a nitrogen and phosphorus or nitrogen, phosphorus and boron fire retardant solution, wherein a mass ratio of the fire retardant solution to the chitosan silver complex is 100:0.1-1. In the other aspect, the invention discloses a preparing method for the mouldproof and inflaming retarding composite wood modifier, that is, the chitosan silver complex and the fire retardant solution are respectively prepared, and are then mixed proportionally to obtain the modifier; and the invention discloses a method for processing wood by using the mouldproof and inflaming retarding composite modifier, which comprises performing vacuum dipping treatment and redrying treatment on the wood. A wood mouldproof technology and a wood inflaming retarding technology are combined to prepare the modifier having both the mouldproof and inflaming retarding characteristics and the modified wood, production efficiency of wood modification is improved, and use safety and an additional value of a product are increased.