Abstract: The design of safety coefficient of thickness for long-distance pipeline is based on some recommanded formula, and the corrosion allowance of thickness itself is a fuzzy value. If the coefficient is insufficient in design, the operation of pipeline will not be safe, and on the contrary, it will not be cost-effective in pipeline investment. On the basis of the method of fuzzy synthetical evaluation, the evaluation model and evaluation method have been established for the optimal pipe thickness of long-distance pipeline. In this paper, a case analysis on the fuzzy synthetical evaluation has been carried out.