［Objective］ The hydrochemical and isotopic characteristics of spring in Baicheng basin were analyzed， the transformation relationships among spring， river water， and phreatic water was identified， and the formation mechanisms of spring were explored to provide a theoretical basis for the rational development and utilization of water resources in Baicheng basin. ［Methods］ Spring samples from the Baicheng basin were collected and analyzed. Comprehensive methods， including Gibbs diagrams， the PCA-APCS-MLR model， and hydrogen-oxygen isotopes， were used to quantitatively assess the transformation between spring and other water bodies and analyze the sources and formation mechanisms of the spring. ［Results］ ① The hydrochemical type of spring water was mainly of HCO₃·SO₄·CL-Ca·Na type， and the spring water was frequently transformed with phreatic water and river water. ② The chemical components of the spring， including Ca²⁺， Na⁺， Mg²⁺， and SO₄^2-， primarily originated from the weathering and dissolution of gypsum and other salts， while Na⁺ and Cl^- were derived from the weathering of silicate minerals such as albite and montmorillonite. Agricultural， industrial， and domestic activities significantly influenced nitrate levels in the spring. ③ The δD and δ¹⁸O values of the spring ranged from -81.28‰ to -50.27‰ and -12.20‰ to -8.57‰， respectively. The δD and δ¹⁸O values of phreatic water and spring in the southern Baicheng basin were generally more depleted than those in the north. This was attributed to substantial recharge from river water. ④ The transformation relationships between surface water and phreatic water in the basin mainly involved river water recharging phreatic water and spring. The recharge proportions of river water and phreatic water to spring were 8.3%—50.1% and 49.9%—91.7% in the middle reaches of the Muzati River and the upper reaches of the Kezier River， respectively. ［Conclusion］ Spring in Baicheng basin are primarily classified as erosional and overflow-descending spring. In the northern high mountainous area， atmospheric precipitation and snowmelt infiltrate bedrock fractures to form phreatic water. Phreatic water emerged as erosional descending spring， mainly distributed in the upper to middle reaches of the Muzati River， owing to the river and floodplain erosion of Quaternary porous aquifers. Phreatic waterthat formed in high-mountain areas was discharged as surface water where rivers or valleys intersected the aquifer. This surface water infiltrated the plain area and was converted back into phreatic water. During migration， phreatic water encountered relatively impermeable layers composed of Neogene mudstone， sandstone， and conglomerate， causing water levels to rise and form overflow descending spring， predominantly located in the middle-lower reaches of the Muzati River and the lower reaches of the Kezier River.