Abstract: The low-temperature release mechanism of fission gas Kr and Xe has been studied.A model has been developed to calculate the pellet chamfer surface average release efficiency,based on the recoil micro-mechanism model of Wise,by considering the effect of pellet chamfer.After that,a more detailed micro-mechanism model of fission gas low-temperature release has been developed,using the knockout micro-mechanism model of Olander for reference,which can be applied to the final fission gas low-temperature release model.