The invention discloses a low-dosage environment-friendly rebar corrosion inhibitor which is characterized by being prepared by mixing one or more phosphates of sodium monofluorophosphate, sodium pyrophosphate, sodium hexametaphosphate and aluminum tripolyphosphate, wherein the sodium monofluorophosphate accounts for 0-10%, the sodium pyrophosphate accounts for 0-30%, the sodium hexametaphosphate accounts for 0-50% and the aluminum tripolyphosphate accounts for 10-100% all by mass. The corrosion inhibitor has the following advantages: 1) the concrete porosity can be reduced, and the permeation rate of a corrosive medium in concrete is slowed down; 2) with low dosage, obvious influence on the working performance such as mixing property, slump and initial setting time of concrete is avoided, the corrosion inhibiting effect on rebars in concrete is obvious, and the corrosion inhibitor can be applied to the repairing of new seaport wharfs, cross-sea bridges, offshore wind power and old ocean concrete structures and the like; and 3) the environment-friendly rebar corrosion inhibitor has the advantages of obvious corrosion inhibiting effect, small dosage and no nitrite.