The invention provides a method for describing the dynamic accumulating and escaping reservoir forming process of thickened oil-shallow gas reservoirs. The method comprises the following steps: 1, describing how natural gas is generated and how the natural gas escapes from an oil reservoir; 2, analyzing a migration and transport way of the natural gas from escape from a thickened oil reservoir toaccumulation in a shallow gas reservoir; 3, inferring the natural gas accumulating reservoir forming period by these fluid inclusion analyzing means; 4, calculating the diffusion coefficient of shallow natural gas through analytical test data of the temperature, the viscosity and the permeability, and calculating the escaping half-life period of the shallow gas reservoir on such basis; 5, predicting the beneficial buried depth of the shallow gas reservoir and the preservation capacity of an original gas reservoir according to a gas producing condition, the diffusion speed, the reservoir forming time and the escaping half-life period. By the method for describing the dynamic accumulating and escaping reservoir forming process of the thickened oil-shallow gas reservoirs, the beneficial buried depth of the shallow gas reservoir and the preservation capacity of the original gas reservoir can be described or predicted according to the scale, the buried depth and the geological condition ofthe thickened oil reservoir in an industrial research area, and an important significance in shallow gas reservoir exploration is achieved.