Abstract: Forest graybrown soil is distributed in an area where Picea crassifolia grows in the midmountain zone of northern slope of the Qilian Mountains. In this study, P. crassifolia forests at altitudes of 2 900-3 000 m. in the Pailugou Drainage Basin in the Qilian Mountains were selected as the research objects, and 3 sample plots were designed every 100 m altitude gradient. Soil nutrient content and pH value under P. crassifolia forest at different altitudes and different soil depths were measured, and their relationship were researcehd. The results were as follows: (1) In the altitude gradient, the average contents of organic matter, total nitrogen and total phosphorus in soil layer of 0-40 cm at high altitude were higher than those at low altitude, and the difference was significant （P<0.05）. However, the contents of soil total potassium and available potassium at high altitude was lower than those at low altitude, and the difference was also significant（P<0.05）. There was no obvious change of available phosphorus content with the increase of altitude, and the difference was not significant （P＞0.05）.  Soil pH value was decreased with the increase of altitude, and the difference was not significant neither （P＞0.05）.  (2) In different soil depths, the average contents of organic matter, total nitrogen, total phosphorus, available phosphorus and available potassium in soil layer of 0-10 cm were higher than those in soil layers of 10-20 cm and 20-40 cm, and those in soil layer of 0-10 cm were significantly higher than those in soil layer of 20-40 cm （P<0.05）.  Soil pH value and total potassium content were increased with the increase of soil depth, the pH value difference between soil layers of 0-10 cm and 20-40 cm was significant （P<0.05）,but the difference of total potassium content among different soil layers was not significant （P＞0.05）.  (3) The correlation analysis of different soil nutrients and pH value revealed that the soil pH value and soil organic matter content were the dominant factors affecting nutrient supply of P. crassifolia  community in cycles of carbon, nitrogen, phosphorus and potassium.

Key words: Picea crassifolia[ forest, altitude gradient, soil nutrient, Pailugou Drainage Basin, Qilian Mountains