The corrosion rate of steel embedded in concrete is evaluated using polarization resistance assumed on the boundary between concrete and steel. However, the previously established polarization resistance method requires the removal of the concrete cover to connect the steel with a wire lead, and it takes a long time for the measurement of corrosion. This study proposes a new method for the nondestructive testing of deterioration caused by corrosion in concrete structures by estimating the surface resistivity of steel. For this purpose, the resistivity on the surface of a steel bar is assumed to behave similarly to the polarization resistance with the progress of corrosion. The resistivity of the steel surface is estimated using the resistivity estimation model (REM), and it is used as an index of the corrosion state. The REM is a mathematical model that considers geometric factors influencing the measurement, such as the cover depth, reinforcement radius, and electrode interval, and it can be used to estimate the resistivities of the concrete and steel bar in concrete structures. In addition, the possibility of applying this resistivity estimation method is investigated by performing an experiment on the accelerated corrosion of steel.