Shale is a strongly heterogeneous anisotropic porous medium with a complex nanopore structure. Therefore, accurately describing the distribution and occurrence of shale gas in the intricate pore structure of shale is difficult. The simplified local density (SLD) theory constitutes an effective and widely accepted approach for characterizing the adsorption mechanism within the intricate pore structures of nanoporous shale. On the basis of SLD theory, this paper proposes for the first time a new adsorption model that considers spherical pores to accurately describe the adsorption behavior within the complex pore structure of shale containing spherical pores. Compared with conventional adsorption theory models and traditional SLD models, not only were the accuracy and applicability of the new model verified, but it was also found that the new model could significantly improve the effective calculation accuracy even with fewer fitting parameters. Furthermore, an analysis of and discussing the adsorption behavior of methane in shale pores with different pore structures (including pore geometries, specific surface areas, diameters and volumes) revealed that the pore structure significantly affects the adsorption behavior of methane. The effects of the number of pore wall solid molecular layers that characterize different fluid-solid interactions and the adjustable parameters for repulsive forces that characterize different fluid-fluid interactions on the methane adsorption isotherms and density distributions were also explored. The results indicate that the newly developed spherical SLD model may provide new insights into the occurrence mode of shale gas in complex shale pores and offer valuable references for reserve assessment and extraction efficiency optimization in shale gas exploration