Abstract: A new method based on fault tree analysis and rough set theory to identify risk is proposed aiming at the status that qualitative analysis prevails over present risk identifications mostly, which lacks objective evaluation. After all possible factors influencing pipeline security are discovered by means of fault tree analysis, attribute reduction may be carried out using attribute reduction algorithm in rough set theory, and finally all risk factors influencing urban gas pipeline security are identified. The method will provide essential basis for risk analysis and appraisal.