A corrosion detection method using galvanostatic transient measurement of grounding grid is proposed to realize the corrosion state detection under the condition of continuous power and no excavation. First of all, the sensors are used to simulate the corrosion of grounding grid, and collect the electrochemical transient detection signal. Subsequently, the noise of the detection signal is filtered out via adaptive wavelet filtering algorithm, which integrates the adaptive threshold selection method into the wavelet filtering and dynamically sets the threshold of each decomposition layer. Finally, the polarization resistance is obtained using galvanostatic transient measurement technology and least squares fitting algorithm, thus the corrosion rate and average corrosion depth can be calculated. Practical field test indicates that the test results of the proposed method are consistent with the on-site excavation. Compared with the linear polarization method, the minimum error only 1.05%, whereas the maximum error of 7.61% is also in the acceptable range. What’s more, the signal-to-noise ratio of the filtered signal is greatly enhanced. In summary, this method has high detection accuracy and good filtering effect, which provides great promise in the practical engineering of grounding grid.