The invention discloses a method for preparing high-purity low-chlorine electroplating-grade cupric oxide. According to the method, copper, liquid ammonia and high-purity carbon dioxide are taken as raw materials, stronger ammonia water is prepared firstly, carbonated ammonia water is obtained through introducing the high-purity carbon dioxide into the stronger ammonia water and controlling carbonization degree, the carbonated ammonia water reacts with the copper under certain air pressure so as to prepare copper-ammonia complexation liquid, the copper-ammonia complexation liquid is then subjected to heating, ammonia distilling, separating, washing, drying and sieving so as to prepare high-purity heavy basic copper carbonate, and the heavy basic copper carbonate is then subjected to heating calcination and decomposition, thereby preparing the high-purity low-chlorine electroplating-grade cupric oxide. According to the method, the carbon dioxide is directly used as a raw material, so that the problems of the traditional method that impurities, such as heavy metal ions and chloride ions, are introduced by raw materials used in the production of basic copper carbonate are solved, the rate of reaction is increased, the production cycle is shortened, the production efficiency is greatly increased, and products are low in impurity content, high in purity, high in activity and wider in application; and meanwhile, the method is high in yield, low in energy consumption, and low in cost and hardly causes pollution.