The invention relates to a phosphorus-free composite corrosion and scale inhibitor for bitter circulating water and a preparation method thereof, belonging to the technical field of water treatment. The phosphorus-free composite corrosion and scale inhibitor for bitter circulating water is prepared from the following raw materials in percentage by weight: 5-20% of sodium molybdate, 5-20% of urotropine, 10-30% of polyepoxysuccinic acid, 1-5% of azole derivative, 5-20% of hydroxypropyl methacrylate, 5-15% of acrylic acid-acrylate-sulfonate terpolymer, 5-15% of sodium humate, 0.1-1% of fluorescent tracer, 0.5-2% of caustic soda flakes and the balance of deionized water. The phosphorus-free composite corrosion and scale inhibitor for bitter circulating water can not interfere with other water treatment agents, is free of phosphorus, zinc and other components harmful to the environment, and can effectively solve the problems of corrosion and scales in the bitter-based high-salt-content high-pH system. The invention also relates to a simple and convenient preparation method.