Based on the statistical analysis from a great deal of failure cases, generally, the failure causes of buried pipeline can be classified into four factors, namely, third-party damage, erosion–corrosion damage, design and construction error, and incorrect operation. The factors influencing the failure of pipeline are complicated, varied and fuzzy. Especially, the influence factors of third-party damage of buried pipeline are of the character of fuzziness, which are difficult to express with the accurate mathematic models. In this paper, the failure factors of buried gas pipeline are first analyzed by fault tree analysis method. Then, the failure likelihood and failure consequence, two parts of the risk, are evaluated with fuzzy comprehensive assessment method, respectively. Finally, the in-service risk of the buried gas pipeline for a certain city is expressed by the risk matrix, which is established with the failure likelihood as vertical ordinate and the failure consequence as horizontal ordinate. It is concluded that there are two pipeline units belong to high risk category, 24 pipeline units belong to medium-high risk category, 160 pipeline units belong to medium risk category, and 392 pipeline units belong to low risk category.