External bonding of fiber reinforced polymer (FRP) composite with epoxy interlocking (EB-FRP-EI) enhancement has been proved to be able to significantly improve the strength of FRP-to-concrete joint according to experimental studies. However, there is no reliability-based analysis to study the effects of epoxy interlocking on the reliability index of FRP-concrete joint. This study investigates the effects of the number of grooves and the depth of each individual groove on the performance of external bonding of FRP composite with epoxy interlocking enhancement by reliability analysis. The reliability analysis of the strength of FRP-concrete joint with epoxy interlocking was conducted by utilizing first order reliability method (FORM). The results show that increasing the depth of each individual groove and number of grooves could significantly increase the reliability index value. For given FRP and concrete, there should exist a most effective and economical epoxy interlocking enhancement design with proper combination of depth of individual groove and number of grooves.