Abstract: Zirconium alloy cladding of fuel rod will be brittle in loss of coolant accident (LOCA), and the brittle cladding is prone to rupture during the accident or the subsequent treatment of the accident causing the release of radioactive products. In this paper, the residual plasticity of homemade Zirlo alloy at cooling rates of 400, 13.3, 4 and 2 ℃/s cooling from 1 200 ℃ to 800 ℃ after LOCA was studied. The results show that the residual plasticity of Zirlo alloy increases with the decrease of cooling rate. The microstructural analysis results by metallographic examination and EPMA show that the oxygen content of prior-β phase decreases with the cooling rate decreasing. The obvious rearrangement of Nb and Fe is observed, which makes the grain refinement of prior-β phase. The combination of these two factors results in the increase of residual plasticity of cladding material.