Due to the uncertainty of variables in durability model, the probabilistic approach is increasing. Monte Carlo Simulation (MCS) is an easily accessible method, but requires a lot of repeated operations. This paper evaluated the effectiveness of First Order Second Moment method (FOSM), which is more convenient and time saving method than MCS, to predict the corrosion initiation in harbor concrete structure. Mean Value First Order Second Moment method (MV FOSM) and Advanced First Order Second Moment method (AFOSM) are applied to the error function solution of Fick's second law modeling chloride diffusion. Reliability index and failure probability based on MV FOSM and AFOSM are compared with the results by MCS. The comparison showed that AFOSM and MCS predict similar reliability indexes and MV FOSM underestimates the probability of corrosion initiation by chloride attack. Also, the sensitivity of variables in durability model to failure probability was evaluated on the basis of AFOSM. The results showed that AFOSM is a simple and efficient method to estimate the possibility of corrosion initiation in harbor concrete structures.