The corrosion behaviors of Q235 steel coupons were investigated via immersion and in-situ volumetric curve in soils with various moistures. The volumetric curves showed that the corrosion process of steel in the soils was a combination of activation and diffusion control. The cathodic part of the polarization curve obeyed Tafel law. Its extrapolation to the corrosion potentials gave the instantaneous corrosion rates much bigger than the average corrosion rate from mass loss. Nevertheless, both of the average and the instantaneous corrosion rates not only showed moisture had significant effect on soil corrosion of Q235 steel but the biggest was in 26% moisture soil being ca. 1.5x of the corrosion rate in the 12% moisture soil. The average corrosion rates for 7 days exposure were bigger than 21 days, owing to more corrosion products accumulating on the surface and hindering mass transfer at longer exposure than at initial immersion. Maximum pit depth grew fast and pit-covered length in per millimeter on the surface of the coupons (L-pit) slow during the first two exposure durations, and they were reversed during the third exposure duration.