Abstract: Gymnodiptychus pachycheilus, a fish species endemic to upper Yellow River's plateau cold-water environments, was listed as a Class II nationally protected animal species in China in 2021．Its current wild population status remains unclear．From August 2023 to October 2025, seven sampling sites were established in upper reaches of Yellow River, where a total of 203 specimens weighing 79521.9 g were collected．Otolith and vertebral age determination, body length-weight measurements, regression model fitting, and microscopic examination of intestinal contents have been used to systematically analyze species' population structure, growth traits, and dietary habits．Results have shown that spatial distribution of Gymnodiptychus pachycheilus was highly aggregated, with 89.66% of individuals concentrated in river section of Lajia Town, Maqin County, Qinghai Province．Most individuals captured in this reach had gonads developed to stages IV to V, suggesting that this section may be a key spawning ground．As for age structure, population was dominanted by 7 to 9 year-old individuals（67.12%）, while 3 to 4 year-old and 6 year-old individuals made up a small proportion（32.88%）, reflecting weak natural recruitment capacity and limited resource recovery potential．In terms of growth traits, length-weight relationship was described by power function W=0.00002L^2.8962（R²=0.9926）, indicating a slow-growing, slender body shape with negative allometric growth（b <3）．Growth inflection points for body length and body weight occurred at 7.2 and 6.1 years of age, respectively．Combined with sexual maturity at 6 years, a gradual shift in energy allocation from growth to reproduction prior to entering the reproductive phase has been demonstrated．Regarding dietary habits, diet was composed primarily of diatoms（52.49%）, green algae（23.52%）, and cyanobacteria（16.81%）, with animal matter accounting for only 5.32%, indicating a pronounced herbivorous dietary habit．This study is the first to systematically clarify population structure, growth traits, and dietary habits of Gymnodiptychus pachycheilus in upper Yellow River, providing essential baseline data for species conservation, sustainable management, and artificial propagation technique development．