The invention discloses a method for preparing silver/silver chloride composite nanocubes. The method comprises the following steps: by taking poly(allylamine) hydrochloride as a stabilizer, firstly, adding certain ratios of silver nitrate and sodium chloride or potassium chloride to synthesize silver chloride nanocubes, and performing diglycol reduction on the obtained silver chloride nanocubes, thereby obtaining the silver/silver chloride composite nanocubes. By adopting the method, a relatively long reaction time is not needed, a complex pH regulation process is not needed, the operation is simple, the amount of reduced Ag is effectively controlled by controlling the reduction reaction time, then the silver/silver chloride composite nanocubes which are high in yield, high in purity and controllable in component are prepared, and moreover the obtained nanocubes are regular in shape, uniform in size and applicable to large-scale production.