It has long been a focus of academia to estimate the soil organic carbon content of forests and to study its influencing factors. The forest soil organic carbon distribution may be present on a hydrothermal gradient; however, most work carried out in mixed forests cannot accurately reflect the variation of forest soil organic carbon along the hydrothermal gradient due to an inability to distinguish the effects from multiple community types. The Picea schrenkiana forest is a pure forest (lower elevation from 1750m above sea level to 2760m at its upper limit), presenting zonal distribution on the huge Tianshan Mountains with variable soil organic carbon along the hydrothermal gradient. So effects caused by community type changes of mixed forest can be excluded. This study set a series of plots and samples along an altitudinal gradient on Picea schrenkiana. It used a potassium dichromate-oxidation external heating method to test soil organic carbon content, discusses the distributional law of soil organic carbon density along the altitudinal gradient, and analyses the impacts of hydrothermal ration and plant community (biomass) on this law. The results showed that: In 1m depth standard soil profile, the soil organic carbon density of each altitudinal gradient presented a decreasing trend with increasing profile depth; the soil organic carbon of each altitudinal gradient was mainly concentrated on the soil surface at a depth of 0-40cm, accounting for about 60%-70% of the whole section. It had obvious surface assembly; the total soil organic carbon density of the standard profile, which peaked on the middle part of the north slope of the Tianshan Mountains' forest, from the lower elevation limit to the upper limit presented an indistinctive bimodal change which decreased, increased and then decreased further. The peaks appeared at an altitude of 1800-2000m and 2400-2600m; the organic carbon density at an altitude of 2600-2800m reached a minimum. The average diameter at breast height of the Tianshan Mountains' forest at different altitudes showed a trend that decreased then increased and then decreased again, consistent with the soil organic carbon density variation law. The variation of soil organic carbon density along the elevation results from the combined action of hydrothermal gradient variation and affected forest growth.