Abstract: This paper is concerned with quantitative risk assessment of oil and gas pipelines. The quantitative risk assessment composes of five components, such as system description, hazard identification, frequency analysis, consequence analysis and risk estimation and evaluation. And this paper describes every component of risk assessment in detail. Risk assessment is a novelty management technique, which has been investigated in U. S., Canada and Europe for many years, having achieved significant societal and economic benefits when applying to pipeline industries. Due to difference between domestic pipeline present conditions and that of overseas, the overseas investigation results of risk assessment may not be applicable to domestic pipeline completely. It is necessary to evaluate domestic pipelines safety according to pipeline practice. In doing so, manager of pipelines can predominate pipeline condition and know danger section in advance, therefore, allotting limited maintenance capitals effectively and improving pipelines safety. In addition, some useful conclusions obtained during risk assessment can provide a basis for pipeline safe design, choosing appropriate run route.