In order to simulate the coupling action of salt-spray environment and fatigued alternating load exactly,the national first marine environment-dynamic load coupling test equipment,which consists of a loading device and an environmental cabinet,was developed.Then,a series of experiments were carried out on nine reinforced concrete ( RC) beams under nine kinds of working conditions to test the parameters including loading frequency and beam's stress level.Experimental results show that ( 1) at the same loading frequency and depth,the greater the stress is,the larger the content of chloride ions is; ( 2) in a stress level of 0. 30 or 0. 50,greater loading frequency may result in larger diffusion coefficient; and ( 3) the penetration of chloride ions in the tensile area is more evident than that in the compressive area.From the comparison of the tested chloride diffusion coefficient D values of concrete with the ones calculated by the empirical formula for static load,it is found that loading frequency has an obvious influence on the penetration of chloride ions of the beam.