To realize the durability health monitoring of the concrete structures,a new technique based on the refractive index characteristic of long period fiber grating(LPFG)to measure the corrosion of steel on concrete structures is proposed in this paper.A notch-shaped pedestal is designed and a long period fiber grating is laid on the steel surface.With this method,the Cl-concentrations of the steel resulting from the steel corrosion would be transformed into the refractive index of the long period fiber grating.The corrosion rate of steel could be obtained by analyzing the change of the spectrum,and then the steel corrosion depth could be measured.From the experiment,it is found that the corrosion rate reaches 12.6%,and the surrounding refractive index changes to 1.353 6 which is within the monitoring range of the LPFG.And the relationship between the wavelength shift and the corrosion rate is obtained.This measurement could be used to monitor the early to medium term corrosion of reinforcing steel in concrete structures.