Investigating the dynamic changes of non-structural carbohydrates (NSC) in Picea schrenkiana is crucial to elucidating the mechanisms of carbon storage and allocation in temperate montane coniferous forests. This study investigated the seasonal dynamics of non-structural carbohydrates (NSC) in Picea schrenkiana forests on the northern slopes of the Tianshan Mountains. From August 2023 to September 2024, we collected monthly samples (13 sampling events total) from different organs (leaves, branches, and roots) and measured soluble sugar (SS), starch (ST), and total NSC concentrations. Our results indicate the following: (1) Significant seasonal variations in NSC concentrations were observed across different organs of Picea schrenkiana, with the most pronounced seasonal variation in soluble sugars in roots and starch in leaves, with coefficients of variation of 63.67% and 67.44%, respectively. (2) Soluble sugar concentrations across all three organs primarily accumulated during autumn and winter, while starch contents decreased in winter and increased in spring. Additionally, the ratio of soluble sugars to starch was higher during autumn and winter, and lower during summer, reflecting seasonal growth and osmotic regulation. Moreover, soluble sugars constituted the dominant fraction of NSC across all three organs, demonstrating their primary role in osmotic regulation under drought and cold stress conditions. (3) Significant positive correlations existed in soluble sugar concentrations among different organs (P < 0.05), while significant negative correlations were found between leaf soluble sugars and leaf starch (P < 0.001), and between root soluble sugars and starch concentrations in leaves and branches (P < 0.05). These findings suggested inter-organ transport of soluble sugars and interconversion between starch and soluble sugars. Collectively, our results provided theoretical foundations for understanding carbon metabolism and growth strategies in Tianshan forest ecosystems.