Abstract: Hoop tensile test is performed on N36 zirconium tube ring specimen at 350℃ to study the iodine induced stress corrosion cracking（I-SCC） behavior of zirconium tube in iodine gas environment, and the stress-elongation curve in partial pressure of iodine gas as 10² Pa,10³ Pa,and 10⁴ Pa separately are drawn. Stress-elongation curve can evaluate the I-SCC susceptibility of zirconium tube. There is no obvious necking stage in stress-elongation curve when I-SCC occurs, and the stages corresponding to crack begins and propagates can be found in the curves. Elongation and fracture energy decrease because of I-SCC, and with higher iodine contents, it decreases even more. Groups of cracks propagate parallel to the fracture surface, and the intergranular crack is located at the edge of crack.