Abstract: With the introduction of the “dual carbon” goals, the coal industry in Chongqing has largely exited, and many coal mines have closed, leaving behind significant amounts of coalbed methane (CBM) resources. These resources and their safety properties are gradually gaining attention. To assess the resource potential of the leftover coalbed methane at Songzao Coal Mine, UDEC software was used to simulate the spatial distribution characteristics of the overburden fracture field in the inclined coal seam mining area. Based on this, a method for calculating the volume of the inclined coal seam gob area and an evaluation method for the leftover coalbed methane resources in closed mines were developed. The fractures in the overburden of the inclined coal seam group due to repeated mining are asymmetric and non-isosceles trapezoids. The fractures in the middle of the gob area are compressed and closed, while the mining fractures mainly occur at both ends of the working face. Moreover, the scale, aperture, and connectivity of the mining fractures at the top of the working face are significantly higher than those at the bottom. An “O”-shaped ring forms around the gob area, with the top being the enrichment region for the leftover coalbed methane. As the coal thickness increases, the mining fracture rate (2.28%, 2.60%, and 3.09%) and fractal dimension (1.087, 1.202, and 1.458) of K2B, K1, and K3B coal seams increase overall. Based on the constructed volume calculation model for the inclined coal seam gob area, the gob volume of Songzao Coal Mine is estimated to be 41.7541 million m³, mainly distributed in the rectangular body area of the gob. The volume of the wedge-shaped pentagonal collapse zone and fracture zone on the side of the final mining line at the top of the working face is 1.40 times and 1.36 times that of the wedge-shaped pentagonal area at the bottom. The evaluation process for the leftover coalbed methane resources at Songzao Coal Mine is constructed in a “classification-zone (horizon)-source overlay” manner. The total amount of leftover coalbed methane is estimated to be 1.299 billion m³, with in-situ, gob, and water accumulation areas accounting for 91.11%, 7.84%, and 1.05%, respectively. The K1, K2B, and K3B coal seams account for 35.58%, 3.21%, and 61.21%, respectively. The coalbed methane in the in-situ and gob areas is mainly in adsorbed form (92.34% and 78.73%), primarily hosted in the K3B coal seam (60.97% and 52.09%). The leftover coalbed methane in the gob area is mainly distributed in the first horizon (47.38%) and second horizon (38.06%), with free coalbed methane predominantly located in the fracture zones of the gob area (82.55%).