[Objective] This study aims to investigate the variation characteristics of soil organic carbon（SOC） fractions and their stability in arid valleys，clarify the relationships between environmental factors and SOC fractions as well as stability，and provide a scientific basis for systematic carbon sequestration and emission reduction management in ecologically fragile areas. [Methods] Soil samples（0―30 cm depth）were collected from different slope aspects（shady，sunny，semi-shady，and semi-sunny slopes）and slope positions（lower， middle，and upper）in the arid valleys of Bomi，Xizang. Soil physicochemical properties，SOC contents，and its fractions were measured. [Results] 1）The SOC content on shady slopes ranged from 11.37 to 34.74 g/kg， representing increases of 55%，138%，and 292% compared with semi-shady，semi-sunny，and sunny slopes， respectively. The contents of particulate organic carbon（POC），easily oxidizable organic carbon（EOC），mineral-associated organic carbon（MAOC），and dissolved organic carbon（DOC）all exhibited consistent variation trends with SOC across different slope aspects. SOC stability was the highest on shady slopes（54.3%-62.1%），exceeding that of semi-shady，semi-sunny，and sunny slopes by 6%，12%，and 30%，respectively. 2）Along slope positions， SOC content decreased in the order was lower slope（17.29 g/kg）>middle slope（13.42 g/kg）>upper slope （9.73 g/kg）. Similarly，POC，EOC，MAOC，and DOC contents all decreased with increasing slope position. The stability of SOC across different slope positions followed the pattern was lower slope（38.1%-62.1%）>middle slope （36.9%-59.9%）>upper slope（37.6%-58.7%）. 3）The main environmental factors influencing SOC fractions and their stability in the arid valleys of southeastern Xizang were slope aspect，vegetation coverage，soil total nitrogen （TN），alkali-hydrolyzable nitrogen（AN），total phosphorus（TP），and clay content. [Conclusion] Significant differences exist in SOC fractions and their stability across different slope aspects and positions in the arid valleys of southeastern Xizang. The key regulatory factors include slope aspect，vegetation coverage，total nitrogen， alkali-hydrolyzable nitrogen，total phosphorus，and clay content. These findings provide valuable references for accurate SOC assessment and soil carbon pool management in arid valleys of southeastern Xizang.