The comprehensive evaluation of pipeline loess collapsibility risk is a necessary means to grasp the safety risks of pipelines in the collapsible loess section, and it is also one of the key scientific basis for risk prevention, control and management. The comprehensive evaluation system of cloud theory consists of quantitative and qualitative indexes, and the evaluation system has the characteristics of randomness and fuzziness. Aiming at the problem that the common qualitative and semi-quantitative evaluation methods have strong subjectivity in dealing with the uncertainty problems such as randomness and fuzziness of the system, the cloud theory, which can effectively reflect the randomness and fuzziness of things at the same time, is introduced, and the state scale cloud and index importance weight cloud of pipeline loess collapse risk are constructed by golden section method. The uncertainty cloud reasoning process of the quantitative indexes and the expert scoring method of the qualitative indexes are proposed. The comprehensive evaluation model of loess collapsibility risk of oil and gas pipeline is established and the engineering example is analysed. The comprehensive evaluation results of 10 samples to be evaluated are basically consistent with the results of semi-quantitative method, and are consistent with the actual situation. The evaluation process softens the hard division of index boundary, simplifies the index data pre-processing, realizes the organic integration of quantitative and qualitative, integrated decision-making, and improves the accuracy, rationality and visualization of the results.