Abstract: As the development targets of offshore oil and gas fields transfers to deep sea areas, the deep-water flow assurance is faced with enormous challenges. The analysis on the formation probability of hydrate in natural gas pipelines is the basis to ensure the safe flow in pipelines. In this paper, the probability limit state equation was established according to thermodynamics and kinetics. In this equation, inlet temperature, pressure and flow rate are taken as random variables after the uncertainty of pipeline operation parameters was investigated comprehensively by means of the reliability based limit state method. Then, hydrate formation probability was calculated by LHS-Monte Carlo method and Proper Orthogonal Decomposition (POD) method. Thus, the risk of hydrate formation in natural gas pipelines can be described quantitatively in the form of probability. It is indicated that the sum of samples which is necessary for stable formation probability curve of hydrate in natural gas pipelines varies with the pipeline circumstances and the random variables. The sensitivity of hydrate formation probability to different random influential factors is different. The formation probability of hydrate in natural gas pipelines is affected more by the critical subcooling. Hydrate formation probability can be reduced effectively by selecting or adjusting the inlet random parameters rationally, so that the safe operation of pipelines can be ensured.