Abstract: This paper introduces the significance of quantitative risk assessment of urban high-pressure pipeline, and concludes that the main reason leading to urban gas pipeline failure is the third-party interference. In order to calculate the failure probability from the third party interference for urban high-pressure gas pipeline, two kinds of failure probability calculation model are proposed, namely, the failure probability calculation method based on correction factor and the subjective correction method of general failure probability. According to actual urban high-pressure gas pipelines, two failure probability values are calculated respectively, and finally the maximum is taking as the failure probability value of quantitative risk assessment. Failure probability of the third party interference calculated by two kinds of models can compare and verify with each other, making the calculation more accurate. This method can provide a reference to the quantitative risk assessment of urban gas pipelines in China.