The invention discloses a corrosion and scale inhibitor for an oil field as well as a preparation method and application of the corrosion and scale inhibitor. The corrosion and scale inhibitor is prepared from the following raw materials in parts by weight: 30-40 parts of cotton hulls, 7-15 parts of tributyl citrate, 0.5-3 parts of melamine cyanurate, 1-5 parts of silicone powder and 18-26 parts of glycerol. The preparation method comprises the following steps: smashing the cotton hulls, adding tributyl citrate solution, heating and stirring, and carrying out microwave treatment; then adding melamine cyanurate and glycerol solution, heating and stirring, and carrying out ultrasonic treatment; and then adding silicone powder, heating and stirring, and carrying out high-temperature calcining, so as to obtain the corrosion and scale inhibitor. The corrosion and scale inhibitor disclosed by the invention has the advantages that the scale inhibition rate can reach up to more than 99% when petroleum produced water serves as reinjection water; and corrosion inhibition rate can reach more than 90%; the preparation method is simple and feasible, conditions are mild, the source of raw materials is wide, and extremely few raw materials are adopted, so that the preparation method can be widely popularized and applied; and the corrosion and scale inhibitor disclosed by the invention has good dispersibility, does not aggregate and is shelf-stable, and the shelf life can reach three years after compounding is completed.