The slab diffusion model based on semi-infinite slab element is usually used to estimate the time to corrosion initiation of RC (reinforced concrete) circular column exposed to coastal atmosphere zone, which ignoring the effect of the circular across-section. The diffusion model considering the diffusion coefficient as time-dependent variable and the effect of circular across-section shape, the influence of the shape of circular RC column exposed at coastal atmospheric zone on the corrosion initiation time is analyzed. The results show that with the coastline increasing and the radius decreasing the overestimation of the corrosion initiation time by using the slab diffusion model is the more obvious. A model for calculating the bearing capacity of corroded reinforced concrete columns is presented, the effect of the radius value on evaluating the degradation rate of bearing capacity of the column at coastal atmosphere zone under different service periods is further discussed. The research results show that the increase of radius result in the reduction of the influence of corrosion on bearing capacity. In the scenario of the RC column located at heavy salt fog zone, the slab diffusion model can be directly used to evaluate the corrosion time. However, in order to control the degradation rate difference value caused by using slab diffusion model within 5%, the effect of shape on corrosion initiation time should be considered when this column is exposed to the light salt fog zone and the radius is less 60cm. And the residual bearing capacity of RC circular column with different service periods is further evaluated.