[Objective] The transformation relationship between surface water and groundwater in Tarim River basin was explored, in order to provide scientific basis for the research on the formation mechanism of water resources and the promotion of rational development and utilization of water resources.[Methods] Using oxygen isotope (δ¹⁸O) as the tracer, the relationship between surface water and groundwater transformation in the Tarim River basin was analyzed by using stable isotope technique and hydrochemical principle. In 2018, about 90 groups of surface and underground water samples were collected along the upper, middle and lower reaches of the Tarim River, and their deuterium oxygen stable isotopes and hydrochemical ions (Cl^-, SO₄^2-, HCO₃^-, Ca²⁺, Mg²⁺, Na⁺) were measured. Gibbs diagram and Piper trigram were used to explore the chemical characteristics and their transformation relationship between surface and underground water in the Tarim River basin.[Results] ① The δ¹⁸O values of groundwater and river water varied differently. For groundwater, the δ¹⁸O values gradually enriched along with the flow direction, while the δ¹⁸O values changed little in surface water. According to total dissolved solids (TDS) analysis along the river, for the upstream groundwater, due to the infiltration and recharging of the river and the influence of lateral runoff, its δ¹⁸O decreased significantly. With the increase of the recharging of the river, its δ¹⁸O value continued to enrich. For surface water, the value of δ¹⁸O gradually decreased with the flow direction, and the groundwater was enriched at this stage, indicating that the groundwater can replenish the surface water during this period. ② The groundwater waterline and river water line were respectively established, both of which were lower than the slope of precipitation line, indicating that the isotopic composition of groundwater and river water was affected by evaporation to a certain extent. ③ The average rate of groundwater recharge to surface water in the upper reaches of Tarim River was 1.76 m³/(d·m), and was 1.71 m³/(d·m) in the middle reaches and 1.65 m³/(d·m) in the lower reaches.[Conclusion] The frequent conversion of surface water and groundwater is the main feature of water resources cycle in Tarim River basin, and groundwater recharge is the main source of water resources.