The corrosion and scale inhibitor is composed of organic phosphonates, copolymers, and copper corrosion inhibitors, and can be used in waters with high pH, high alkalinity, and high hardness. The inhibitor exhibits excellent corrosion protection performance for carbon steel, copper, and copper alloys. It can complex with calcium and magnesium ions in water to form water-soluble complexes that inhibit scaling. It also has outstanding scale inhibition and dispersing properties for calcium carbonate and calcium phosphate, while effectively dispersing impurities such as silt in water, keeping them stably suspended and preventing deposition. This product is mainly used in open recirculating cooling water treatment systems, and is especially suitable for systems containing copper equipment.