To investigate the impact of different sustained load ratios (the ratio of sustained eccentric compressive load to ultimate eccentric compressive load) and different environments on hysteretic behavior and chloride mass fraction of RC(reinforced concrete) columns, the working conditions of RC structures in coastal region were simulated in laboratory. The sustained load ratios were 0,0.2 and 0.35, respectively. After the RC columns with sustained load had undergone 100 cycles of seawater dry-wet or 100 days in atmospheric environment, low cyclic horizontal loading test was conducted and chloride mass fraction in tensile concrete was tested. Results show that sustained eccentric compressive load lead to the apparent asymmetric pattern of the hysteretic curves of RC columns in seawater dry-wet environment or in atmospheric environment. And the asymmetric pattern of former is more apparent than that of latter. While the stress distribution of cross-section under horizontal cyclic loading is the same as that of sustained eccentric compressive load and the sustained load ratio is 0.35, the peak load and the energy dissipation of RC columns in seawater dry-wet environment are 0.89 and 0.57 times of that in atmospheric environment, respectively. But the former are 1.04 and 1.08 times of the latter if reverse cyclic load is applied. In the depth of 20 mm and 40 mm from tensile surface, chloride mass fraction of tensile concrete in the columns subjected the coupled actions of sustained load and seawater dry-wet cycles are more than 3 times of that only subjected to sustained load (the RC columns in atmospheric environment). These clearly imply that the coupled action of sustained eccentric compressive load and seawater dry-wet cycles could facilitate the chloride penetration and hysteretic behavior degradation.