For the need of radiation reliability analysis on the memory devices which were applied in the nuclear facilities, the threshold dose of the floating gate cells in a domestic NOR-type flash memory had been investigated. A reliability analysis method with extremely small sample size had been established by utilizing the SMOTE-Bootstrap algorithm. The experimental results showed that the dominant failure mode of the floating gate cell was the threshold voltage reduction due to charge loss in the floating gate, and the average verification error dose was 631.89±103.64)Gy(Si). The statistical analysis results showed that the radiation damage dose of the device obeyed the lognormal distribution. The SMOTE-Bootstrap algorithm avoided the problem that the conventional bootstrap method would cause an abnormal data concentration in the generated samples. Meanwhile, the algorithm had been proved to be suitable for the application of reliability analysis with extremely small sample size.