Abstract: The plastic layer that forms during the coking process of coking coal is crucial for the stability of the coking operation and the quality of the resulting coke. The low permeability and high swelling pressure of the plastic layer can lead to excessive pushing current during coke pushing, affecting the normal operation of the coke oven. Therefore, the permeability and expansion properties of the plastic layer have become important indicators for measuring the safety performance of coking coal. To explore the evolution of permeability and expansion of the plastic layer during the coking process of coking coal and to extend its application in the evaluation indicators of coking coal, six types of coking coal with different degrees of metamorphism were utilized as research subjects. Solid-state nuclear magnetic resonance carbon spectroscopy (¹³C-NMR) was employed to analyze the molecular structural characteristics of the coal, and thermogravimetric analysis (TGA) was combined to investigate the thermal decomposition behavior of the coal. The study measured the Gieseler fluidity, Audibert-Arnu dilatation, permeability, and expansion pressure during the coal coking process. The study explained the release behavior of volatiles in the plastic interval of the coal, and elucidated similarities and differences between the Audibert-Arnu dilatation and swelling pressure. The results indicate that permeability can comprehensively reflect the changes in the plastic layer. The initial low permeability temperature (T_i) increases with the degree of coal metamorphism. The low permeability temperature zone (ΔT_P) exhibits a quadratic function relationship with the liquid-gas ratio (LGR) and is closely related to the size of the coal molecular structural units. ΔT_P is wider than the plasticity temperature zone (ΔT), attributed to the dense structure of the newly formed semi-coke hindering the release of volatiles. Swelling pressure can compensate for the Audibert-Arnu dilatation degree and is an important parameter for evaluating the expansion behavior of gas coal and lean coal. The initial softening temperature (T₁') increases with the deepening of coalification, and the maximum expansion pressure of the plastic layer (SP_Tmax) first increases and then decreases with the degree of aromaticity. There is a positive correlation between SP_Tmax, expansion volume, LGR, and ΔP.