Abstract: To provide foundation for corrosion protection of the weld metal using in grounding grid, the corrosion difference between the weld and base metal of grounding grid was studied by electrochemical noise and field coupon method. The results showd that there were many transients in the time series of the weld of Q235 steel for grounding grid in soil of Shaanxi Xiaoyi substation, while a few transients in the time series of the Q235 base metal, which indicated that weld corrosion was more sensitive to discharge voltage of grounding grid. The noise resistance of the weld metal, Rn, was 3.38×10⁴Ω/cm² during the corrosion process, and the Rn of the weld was 1.44×10⁴Ω/cm². The corrosion rate of the weld metal was 0.067 mm/a, and for the welded joint was 0.077 mm/a. The based metal was in a uniform type of corrosion and the weld was mainly in a pitting type of corrosion.