When the RC structure degraded in sea environment, chloride ion is one of the most important factors of degradation. Therefore, the purpose of this analytical study is measuring diffusion coefficient of patching repair material and the structure which repaired with patching repair material by RCPT. Also with this experimental result, Finite Element Method (FEM) is used for determining service year of building and concentration of chloride ion in the structure material. As the result of RCPT, diffusion coefficient of patching repair material is 0.44×10-8cm2/sec, which is 18.7% of concrete (3.18×10-8cm2/sec). Meanwhile, as the result of FEM, patching repair material is effective for prevent chloride ion. When service year of normal concrete structure is 16years, on the other hand, the structure recovered 10mm of patching repair material will take 49 years to its service year. Furthermore, the result derived from equation given from JSCE predicts service year of the structure is little bit less than FEM.