Under formation condition, the flow state of shale gas is affected by multi-scale effects, including viscous flow, diffusion flow and slippage flow, etc., gas production is the result of synergy of various mechanisms, and previous diffusion models can no longer accurately describe the diffusion behavior of shale gas in the shales. In order to clarify the influencing factors of shale gas diffusion ability, reveal the flow law of gas wells in the whole life cycle development process as well as the impact on production capacity, experiments on shale gas under the conditions of 0-1 MPa micro-pressure difference is carried out by using the self-developed experimental system with high temperature and high pressure resistance, and put forward a diffusion coefficient calculation method comprehensively considering permeability, temperature and pressure. It was successfully applied to the Wufeng-Longmaxi formations shale in the south of Sichuan, indicating that the critical pressure of the high-quality reservoir in this area is 4.5 MPa when diffusion flow occupy the main position. It is of great significance for the shale gas well productivity evaluation and the quantitative characterization of the diffusion capacity. The experimental results and theoretical analysis show that the diffusion will have a higher partition coefficient under high temperature, low permeability and low pressure level, the diffusion coefficient model considering the permeability of shales can be better applied in actual flow, and there will be a large error in productivity calculation if ignoring the effects of diffusion.