Natural gas pipeline leaks under the sea will have a significant negative effect on the marine ecosystem, result in significant financial losses, and possibly even harm marine floating objects. The VOF (Volume of Fluid) multi-phase flow model is used to numerically simulate and study the diffusion process of porous leakage in submarine gas pipelines. Experiments confirmed the model’s correctness and dependability. Based on this, the coupling effect and the porous effect of the leakage velocity, the size of the leaked pore, and water velocity of the natural gas pipelines on the diffusion of porous leakage in the submarine gas pipelines are analyzed with the test scheme designed by the orthogonal test method. The similarity principle is used to connect the leakage model with the actual application. The results show that three factors, namely, the leakage velocity, the size of leaked pore, and the water velocity, influence the shape of the air mass, the time when the gas reaches the sea surface, and the diffusion range. The size of the leakage hole and the leakage velocity have a substantial impact on the form of the air mass and the amount of time it takes for the gas to reach the sea surface, while the water velocity has no effect. Additionally, while there is essentially little impact from the leakage velocity, the size of the leaky pore and the water velocity have a significant impact on the diffusion range. Furthermore, the porous effect between leaky pores has a significant impact on the gas diffusion range. This study can serve as a guide for risk assessment and emergency decision-making regarding a submarine gas pipeline leak.