The invention relates to a phosphorus-free corrosion and scale inhibitor for use in water treatment equipment. The phosphorus-free corrosion and scale inhibitor comprises the following active components in part by weight: 9 to 10 parts of itaconic acid-acrylic acid-acrylate copolymer, 4 to 5 parts of 2-acrylamide-2-methylpropane sulfonic acid-diethylacrylamide polymer, 4.5 to 5.5 parts of polyepoxysuccinic acid and 5 to 6 parts of hydrolyzed plymaleic anhydride. The active components of the phosphorus-free corrosion and scale inhibitor are natural macromolecular compounds which have a natural ring-shaped structure and characteristics of hydrophilic outer cavity and hydrophobic inner cavity and active groups having high valence metal ion chelation are on the outer sides of the natural macromolecular compounds, so that the inhibitor has a certain corrosion and scale inhibiting property; corrosion and scale inhibiting performance of the inhibitor is greatly improved due to the modification by the advanced technique of multi-disciplines, such as the electrochemistry theory, the quantum chemistry theory and the molecular structure design, molecular weight reduction and the introduction of active groups; and in addition, the inhibitor has the advantages of high corrosion and scale inhibiting performance, no toxin nor harmlessness, stable performance, low price, corrosion resistance, rich raw material sources, easy biological degradation in the environment and the like.