Abstract In terms of the risk from submarine natural gas pipeline leakage, a computational fluid dynamics (CFD) model is developed to predict and assess the consequence of natural gas escape. In the present study, both of the scenarios that natural gas escapes into sea water and above the sea surface are included. The escape trajectory of natural gas in seawater is predicted, and the critical risk parameters like rise time, spill position and spill region etc. are assessed using the developed CFD model. Based on the assessment results of natural gas movement in seawater, the transport process and corresponding danger areas of natural gas above the sea surface are also determined. In addition, considering the likelihood of ignition, the deflagration scenario of natural gas above sea surface is simulated and analyzed in the present study for assessing the overpressure, high temperature and heat radiation, etc. The study results indicate that natural gas escape in seawater could lead the density of surface water to decrease, and form a “boiled” zone or fountain, which would have an effect on the stability of floating structures on sea surface. A deflagration accident may occur when the natural gas above sea surface is ignited by a ship or platform. The CFD model developed in this paper could be employed to predict and assess the risk of natural gas from submarine pipeline leakage effectively, and provide an educational reference for risk management and emergency decision-making for submarine natural gas pipeline leakage.