Tensile test at room temperature and low temperatures for the QLT-treated 9%Ni steel were carried out. The amount and lattice parameters of reversed austenite and the microstructure in the vicinity of tensile fracture surfaces were analyzed using XRD and TEM. The effects of reversed austenite on tensile deformation behavior of QLT-treated 9%Ni steel were investigated. Experimental results show that the uniform elongation increases and the yield ratio decreases when the tensile temperature decreases from 20 to -196℃ in the QLT-treated 9%Ni steel. This indicate that the phase transformation of reversed austenite during the low-temperature tension improve the cryogenic plasticity of QLT-treated 9%Ni steel.