Humus is a complex polymer which decomposes and synthesizes animal and plant residues under the action of microorganisms and is the main component of soil organic matter. Litter nutrient input is one of the main sources of soil humus. However, in subalpine forests, frequent freeze-thaw cycles impact the process of soil humification and litter decomposition. The relationship between litter and soil humification in subalpine forests is fundamental to understand the dynamic process of forest soil organic matter, which is affected by seasonal freeze-thaw cycles, litter decomposition processes, and soil properties. However, there is limited information in this regard. Therefore, based on the pre-recognition of sub-alpine litter humification and seasonal freeze-thaw cycles, taking typical coniferous, coniferous-broadleaf, and broadleaf forest soil in the sub-alpine region of western Sichuan, we controlled the freeze-thaw environment and litter addition, and analyzed the tone coefficient (ΔlogK), optical density value (E4/E6), and A600/C value, which can accurately reflect the degree of soil humification by extractable humus color. The results showed that the freeze-thaw cycles, litter additions, and their interactions all significantly affected the soil humification, but were controlled by the characteristics of litter and soil types. In the early freeze-thaw environment, the addition of litter can promote soil humification processes and improve soil humification. With prolonged freeze-thaw cycles and the continuous decomposition of litter, the broad-leaf litter can promote soil humification, whereas needle litter inhibits soil humification. Moreover, in freeze-thaw environments, soil humus is still relatively young, even though soil humification is increased, which shows that freeze-thaw cycles can improve soil humus quality to a certain extent and help maintain soil fertility. These results show that changes in freeze-thaw cycles under climate change will significantly affect the relationship between litter and soil humus, which provide a scientific basis for better understanding soil organic matter dynamics in subalpine forests.