The invention discloses a nano-zinc oxide-silver-loaded chitosan composite antibacterial agent and a preparing method thereof. The preparing method comprises the steps of dissolving chitosan in acetic acid aqueous solution or formic acid aqueous solution under the condition of normal-temperature stirring, adding polyethylene glycol and hydroxyethyl cellulose in sequence, conducting uniform stirring, adding silver nitrate aqueous solution, conducting uniform stirring for reaction at 100-115 DEG C under the microwave condition, conducting natural cooling to room temperature, adding nano-zinc oxide, and conducting constant stirring at normal temperature till the system becomes transparent so that the nano-zinc oxide-silver-loaded chitosan composite antibacterial agent can be obtained. Reductible hydroxyl of chitosan is used as a silver ion reducing agent, introduction of a new reducing agent is not needed, and a silver-loaded chitosan solution is prepared with the one-step method; by means of microwave synthesis, reaction time is shortened greatly, the reaction system is prepared at normal temperature mostly, obtained nano-silver particles are evenly distributed, and agglomeration is reduced greatly; antibacterial property is excellent, biosecurity is high, the method is simple, and production cost is low.