In order to understand the genetic mechanism of carbon isotope discrimination (Δ) and water use efficiency(WUE) in wheat, we used recombinant inbred lines (RILs) of wheat to study the genetic basis of Δ under different water treatments, based on QTL mapping and environmentspecific assistive effect analysis. The results show that: (1) Δ value in the RILs population showed a normal distribution, indicating that Δ is a quantitative trait. (2) We detected 11 majoreffect Δ QTLs in 2B, 3B, 7B, 1D, 3D and analyzed their phenotypic variation rate between 10.83%-46.87%, 9 additive × environment interactions QTLs and analyzed their phenotypic variation rate between 1.02%-3.15% were detected. (3) We detected 5 pairs of epistatic QTLs which include 3 pairs of epistatic QTLs and their interactions rate between 0.86%-2.01%. (4) Additive effect and contribution rate were larger than epistatic effect and contribution rate, AQTL and AQTL × environment contribution rate were larger than AAQTL × environment contribution rate. The results indicated that the genetic variation of Δ in the RILs population was mainly affected by additive effect QTLs, the majorgenecontrolled Δ has a greater effect than the water environment.