Abstract: Aiming at the confusing basic concepts in the pipeline risk assessment, the authors define some basic terms such as safety, risk, oil & gas pipeline risk, pipeline failure modes, risk assessment, risk analysis, risk management, risk estimate, risk control and risk decision-making etc. The risk analysis model is established, including the system model and process model of quantitative risk assessment. What this study has done consummates and consolidates the essential concepts and system to be advantageous to performing the pipeline risk assessment.