Various reservoir types have been discovered in coal measure gas reservoir. Co-fracturing production of coal measure gas in the same well can enhance resource utilization efficiency. However, the applicability of the same fracturing fluid may vary across different reservoirs, and the methane desorption characteristics is still unclear. This study constructed typical nanopore models of deep coal, shallow coal, and shale by combining the mineral composition and organic geochemical characteristics of coal reservoir rocks. The study investigated the retention characteristics of guar-based fracturing fluid and methane desorption law in different types of pores using grand canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) methods. And the following research results are obtained. First, residual molecules of fracturing fluid in coal reservoirs can be retained in the microporous throat of organic matter, forming a plugging structure. And these molecules can polymerize and adsorb on the surface of pores and cracks, resulting in a concentrated ‘filter cake’. Second, returning guar-based fracturing fluid in inorganic quartz minerals is easier than in coal organic matter, and the flowback difficulty of residual molecules of this fracturing fluid in deep coal is lower than that of shallow coal. Third, in coalbed methane reservoirs, deeper coal seams produce gas earlier and contribute more significantly than shallower coal seams and shale. During the depletion of deeper coal seams, the low recovery of adsorbed methane from micro-pores and cleats represents a key target for enhanced recovery in later stages. This paper examines the adsorption and retention properties of guar-based fracturing fluid and the mechanism of methane desorption in coal reservoirs from a microscopic perspective. The study offers theoretical insights for the selection of fracturing fluids and the dynamic evaluation of production and development.