Oil and gas pipelines have many risk factors, such as third party damage, corrosion, design, and maloperation, which possess many specific risk factors, the least buried depth, ground operations, ground equipment, public education, line status, patrol frequency, and many others. How to determine the weight of each factor accurately is a widespread concern. In this study, the improved three-scale AHP method is introduced to determine risk index weight of pipelines. This method has the advantages of being concise and practical, as well as having a small workload, strong pertinence, and easy-to-compare factor significance, all of which make it more accurate and objective to determine the indexes weights and to conform better to the actual situation. The method proceeds in three steps: first, using improved AHP to determine weight of the two-level index; then, similarly, determining the weight of the three-level index successively; and finally, calculating the weight values of all risk factors.