As an important factor affecting global warming, marine geological disasters, and the safety of marine engineering construction, gas migration in submarine sediments has received a great deal of attention from academia and industry in recent years. This article reviews the growth and migration mechanisms of gas in seafloor sediments and evaluates the existing methods for monitoring of shallow gases. Existing experimental evidence shows that the two forms of gas distribution in sediments, isolated bubbles and continuous gas, have different migration modes. After a bubble undergoes the growth process in the pores of sediments, it will continue to grow through alternating cycles of elastic expansion and tensile fracture until reaching a certain size, at which time it will start to rise under the action of "pseudo-buoyancy." The whole process can be described by the Linear Elastic Fracture Mechanics (LEFM) theory. The migration of continuous gas in sediments mainly occurs through capillary invasion and fracture opening, with the former being found primarily in coarse-grained sediments and the latter in fine-grained sediments. The two migration modes are mainly controlled by sediment grain size, stress, and other factors. The main methods for monitoring gas migration in sediments include Computed Tomography (CT) technology, gas pressure monitoring, pore pressure monitoring, marine seismic methods, and marine resistivity methods. CT technology and gas pressure monitoring are mostly applied at the laboratory scale, while the in-situ measurement of submarine shallow gas is mostly observed by means of geophysical exploration such as the marine seismic method and marine resistivity method.