Pipeline is a major way for natural gas transportation. Accidental gas release from a pipeline might lead to great economic losses and casualties. Therefore, it is important to investigate the dispersion characteristics of natural gas release from pipelines. Most previous studies on accidental natural gas release from pipelines mainly focused on bare pipelines and adopted simplified 2D models. This paper first established dispersion models of natural gas release from buried pipelines with high and low pressure, respectively. The numerical methods were validated by Trial 26 of the Thorney Island field experiment and the dispersion model was found to be reasonable and reliable. Then, comparative study between 2D and 3D dispersion model of released natural gas was carried out, which proved that 3D model had superiority upon the 2D model. Then the 3D model was employed to simulate dispersion process of released natural gas by changing pipeline pressure, orifice diameter, wind speed, and soil properties. Finally, the effect of leakage conditions on consequence distance was analyzed. The numerical results could provide technical supports for the design of emergency disposal equipments and urgent pipeline repairs.