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Gas drainage in boreholes is characterized as an essential means to control abnormal gas emissions during mining. Unfortunately, its drainage efficiency is terribly restricted by high in-situ stress in deep underground coal seams. Gas drainage involves gas emission under stress constraint conditions (SCCs), as well as multi-scale gas migration (gas desorption, diffusion, and seepage). Nevertheless, how SCCs influence gas emission behaviors remains unclear. Considering this status quo, this paper focuses on researching He and CH 4 emissions under different SCCs, and analyzes the influence of SCCs on gas emission by integrating the initial gas diffusion coefficient and the diffusion attenuation coefficient. In addition, a novel method for calculating equivalent diffusion and seepage pore radii by the T 2 spectrum of nuclear magnetic resonance was proposed. Finally, according to the multi-mechanism gas emission model that tracks the dynamic evolutions of the equivalent diffusion and seepage pore radii, the influences of equivalent pore radius and pressure on the conductance of different diffusion mechanisms were further quantitatively analyzed. The research in this paper is expected to provide a theoretical reference for efficient gas drainage in deep coal seams. • The influence of stress on the apparent gas diffusion coefficients was analyzed. • The equivalent diffusion and seepage pore radii were proposed and calculated by NMR. • A multi-mechanism gas emission model considering dynamic pore radius was developed. • A testing method of adsorbed CH 4 desorption amount in fractured coal was proposed. [ABSTRACT FROM AUTHOR]