Abstract: In order to grasp the thickness ratio effect of soft and hard interbedded overburden structure on the cross–fusion of pressure relief gas transportation and storage area, the soft and hard interbedded overburden structure with different thickness ratios was taken as the test object, and the two–dimensional physical similarity simulation experiment platform was used to carry out the crack evolution and breaking mechanism experiment of soft and hard interbedded overburden structure. Combined with the fractal theory, the fracture distribution characteristics of soft and hard interbedded overburden structure were quantitatively described. According to the theory of mining overburden elliptic paraboloid zone, the characteristic parameters such as rotation angle, penetration degree and fracture rate were introduced to study the dynamic change characteristics of cross–fusion of gas migration area and reservoir area in soft and hard interbedded overburden structure affected by the thickness ratio of soft and hard interbedded structure.The experimental results show that the internal and external boundaries of the gas transport–storage area and the transport–storage boundary are located in the mutation areas of fractal dimension, fracture penetration, fracture rotation angle and fracture rate, respectively. The fracture rotation angle of the migration area is greater than 2.07°, and the fracture rotation angle of the reservoir area is 1°～2.07°. The fracture connectivity of gas migration area and reservoir area is 0.6～1.0 and 0.2～0.6, respectively. According to the changes of fracture rate, rotation angle and penetration degree in gas transportation–reservoir area, the boundary of gas migration area, reservoir area and cross fusion area is determined. The fracture rate, rotation angle and penetration degree decrease rapidly at first, then the decrease rate slows down obviously, and finally the decrease rate increases again. The overlying strata of the soft and hard interbedded strata experienced five periods: the formation of the transport–reservoir area, the first appearance of the migration area and the reservoir area, the first formation of the cross–fusion area, the expansion of the cross–fusion area, and the gradual blurring of the transport–reservoir area and the cross–fusion boundary. Finally, a complete elliptical parabolic banded overburden fracture field was formed. The quantitative characterization model of thickness ratio effect of gas transport–storage area in soft and hard interbedded overburden structure is established. At the same time, the boundary and state determination process are determined according to the characterization parameters of gas transport–storage area, and the fracture evolution and fracture mechanism of overlying strata in soft and hard interbedded overburden structure are determined.