With the rapid development of city，the urban pipeline accidents caused by the underground disease occurred. The forming reasons of underground disease around pipeline were researched，and the influence of the underground disease was analyzed on urban pipeline. The risk assessment process was determined. The index system of risk likelihood and consequence was established，and the weight was fixed by expert estimation and AHP （analytic hierarchy process），and the score standard of the typical index was given. This paper provides a scientific method for risk management of urban underground pipelines.