Abstract: The fatigue property of structural members has been changed with varying rainfall distribution. Therefore, an improved regression method for estimating S-N curves of corrosion fatigue is proposed by combining with the single-point group testing method and optimization method of correlation coefficients firstly. And an implementation algorithm corresponding to the improved method for estimating S-N curves is also put forward. According to this improved method, the P-S-N curves expression for different corrosion modes is presented. Meanwhile, there are 39 full-scale Q345 equal angles with three corrosion modes in the same corrosion time are studied by the fatigue test. Through the comparison of results, the corrosion state of specimens with #x0201c;immersion-airing#x0201d; corrosion method is observed. The corrosion fatigue failure modes of specimens are observed and the variation law of P-S-N curves with different corrosion modes is obtained. Combining this improved method, the P-S-N surface model with different reliability levels of Q345 equal angles is proposed for each corrosion mode. At last, the variation law of Q345 equal angles#x02019; fatigue life in each corrosion mode is studied by the proposed P-S-N surface model. It can be found that: 1) The effect of corrosion modes on the fatigue life is becoming more and more serious with the decreasing load in the same corrosion time. 2) The fatigue life is decreasing sharply with increasing reliability levels under the same load if the corrosion is serious.