［Objective］ This study investigated the litter decomposition dynamics and their influencing factors of the dominant species， Larix gmelinii， and its associated species， Betula platyphylla， in the permafrost region of the Great Xing’an mountains， in order to provide scientific insights for maintaining forest ecosystem stability， enhancing carbon sequestration capacity， and formulating adaptive management strategies under permafrost degradation. ［Methods］ A litterbag experiment was conducted using three treatments of L. gmelinii litter （needleleaf）， B. platyphylla litter （broadleaf）， and a combined litter （3∶1 ratio）. Over a two-year in-situ decomposition period， litter mass loss dynamics and their relationships with C and N content were systematically analyzed. The Olson exponential model was used to calculate the times required for 50% and 95% litter decomposition. ［Results］ ① The litter mass loss over the two-year decomposition period was fastest for broadleaf litter （23.53%）， followed by the mixed litter （16.41%）， and slowest in the needleleaf litter （14.47%）， with 65.11%—66.80% of the total mass loss occurring during the first year. The measured mass-loss rates of the mixed litter were significantly higher than predicted in the first year of decomposition， indicating a synergistic effect. ② Broadleaf and mixed litter mass loss showed highly significant positive correlations with N content and negative correlations with the C/N ratio. However， there were no significant correlations between needleleaf mass loss and N content or C/N ratio. ③ The Olson model effectively described the decomposition dynamics （R²>0.89）. The time required for 50% and 95% litter decomposition was shortest for broadleaf litter （5.45 years and 23.55 years）， followed by mixed litter （9.32 years and 40.27 years）， and slowest for needleleaf litter （11.55 years and 49.93 years）. ［Conclusion］ The rapid decomposition of broadleaf litter may be attributed to its high N content and low C/N ratio. The complete decomposition of needleleaf and mixed litter requires over four decades， nearly double the time for complete broadleaf litter decomposition， which requires slightly over two decades. The mixed litter mass loss only exhibited synergistic effects during the first yesr of decomposition. These slow decomposition processes are critical for maintaining the C-N balance in the permafrost-vegetation feedback system and for enhancing the ecological barrier functions of cold region ecosystems.