A novel low phosphorus terpolymer scale inhibitor P(IA-MA-SHP) was prepared by aqueous free radical polymerization using itaconic acid (IA), maleic acid (MA), and sodium hypophosphite (SHP) as raw materials. It was mainly used as an efficient scale inhibitor to inhibit CaCO₃. The structures of the copolymers were characterized by Fourier transform infrared, ¹H-NMR, and ¹³C-NMR, and the thermal properties, and scale sample crystal structure morphology of the copolymers were analyzed by thermogravimetric analysis, x-ray diffraction (XRD), and scanning electron microscope (SEM). The effects of dosage, monomer ratio, temperature, and reaction time on the scale inhibition effect were investigated, and the optimal synthesis conditions were determined. The results show that: when the monomer ratio is n(IA):n(MA) = 1.0:1.0, the mass fraction of SHP is 10%, the amount of ammonium persulfate initiator is 12%, the reaction temperature is 90°C, and the reaction time is 4 h, when the dosage of the agent is 20 mg L⁻¹, the scale inhibition rate of CaCO₃ is 94.30%, while it also has a favorable inhibitory effect on CaSO₄. The results of SEM and XRD show that the copolymer scale inhibitor can distort the lattice and has a favorable adsorption and dispersion effect. In addition, it has a positive effect on controlling the scale.