Abstract: Through research on calculation methods of quantitative risk, the authors introduce the concept of fatal length and give the expression of individual risk, the expressions of calculating pipeline length within different death probabilities at a specified location from a pipeline are deduced.And the criteria applicable to gas pipeline risk evaluation are analyzed as well. Case analysis shows that the fatal lengths at three failure modes are evidently different and become most when the pipe is completely broken. Besides, with the increase of the distance from gas supply station, the fatal length decreases sharply first, and then goes to a balance state. The distribution of individual risk along the pipeline also remains the same state.