Abstract The rebar corrosion monitoring using magnetic method is a hot research area and it is necessary to develop effective methods using the rebar’s own magnetic characteristics with considerations of environmental magnetic field. In this paper, the magnetic gradient and partial modulus is proposed for rebar corrosion monitoring. The effectiveness of corrosion monitoring method is discussed on the basis of experimental results from eight rebars and four reinforced concrete beams before and after corrosion. The other three galvanized round steels are used to investigate the reliability and stability of the method. The results show that the percentage loss calculated by the magnetic gradient and partial modulus is basically consistent with the actual weight loss ratio and cross-sectional area loss ratio for uniform corrosion and the effects of environmental magnetic field can be negligible by using magnetic gradient and partial modulus, which shows promise for medium- and long-term monitoring in rebar corrosion.