A pot experiment of maize was conducted from June 9 to September 25 in 2007, to explore variations and relationships between intercellular CO₂ concentration (C_i), stable carbon isotope discrimination (Δ¹³C) and CO₂ leakage from bundle sheath (φ) during photosynthesis of summer maize in six typical growth stages (seedling, jointing, booting, tasseling, filling, and mature) under different water regimes, using the stable carbon isotope technique and Portable Photosynthesis System (LI-6400, LI-COR, Inc, USA) The plants were subjected to four water regimes, i.e. 75%~100% (Treatment W1), 50%~75% (Treatment W2), 30%~50% (Treatment W3) and 0~30% (Treatment W4) of the field capacity of the soil. Results show that (1) stomas on the summer maize leaf closed under water stress at the jointing stage, which led to lower C_i in Treatments W2, W3 and W4, as compared with that in Treatment W1. At the following growth stages of booting, tasseling and filling, C_i in Treatments W1, W2 and W3 decreased with intensifying water stress; however, C_i in Treatment W4 was higher than in Treatments W2 and W3. Leaf aging sped up and C_i increased with intensifying water stress at the maturing stage; (2) under the joint effect of water regimes and growth stages, in Treatments W1, W2 and W3 Δ¹³C for summer maize leaves displayed a trend similar to that of C_i/C C_a from the jointing stage to the filling stage, but a different one at the maturing stage; whereas in Treatment W4 it did only from the booting stage to the filling stage; no matter in what treatments, Δ¹³C was significantly correlated with φ, which affected Δ¹³C more than C_i/ C_a did; and (3)φvaried in a trend similar to that of Δ¹³C in the maize leaf in all the treatments, however, in Treatments W1, W2 and W3 φ declined with intensifying water stress, while in Treatment W4 it turned upwards.