The hypothesis testing approach was applied to treat the experimental data from the open literature for the establishment of the distribution law of the strength retention rate of fiber reinforced plastic （FRP） stirrups. The goodness-of-fit of three distribution models （Weibull distribution， normal distribution， and lognormal distribution） for the FRP stirrups strength retention rate was compared using Kolmogorov-Smirnov （K-S） test. The results show that the lognormal distribution is the optimal distribution model within the rational range （3-5） of internal radius（R） to bar diameter（D） ratio （R/D）. It follows that the strength retention rates of 95% and 50% guarantee rates is no less than 32.46% and 43.79%， respectively. Furthermore， the results show that the reliabilities of calculation results from the retention rate formula used in the Chinese， American， Canadian， and Japanese standards are only between 24.1%-40.3%， which is unconservative. According to the strength guarantee rate requirements of FRP longitudinal reinforcement and stirrups in China， the strength retention rates of glass fiber reinforced plastic（GFRP） stirrups with R/D of 3，4 and 5 are not less than 38.86%， 35.68% and 46.09%， respectively.