Abstract: Recently, due to their high specific strength, non-electric conductivity, non-magnetic nature and corrosion resistance, fiber reinforced polymer (FRP) bars are being used in engineering structures built in corrosive environments to enhance the durability of reinforced concrete (RC). Moreover, because of their high strength, small elastic modulus and remarkable size effect, the FRP bars are applied to pre-stressed structures, and their stress-relaxation feature is an important design parameter. The anchoring and measuring method for stress relaxation specimens with larger-diameter sand-surface FRP bars is studied. The results show that the modified steel sleeve-type anchoring method can reduce the slippage of the specimens, which meets the requirements of specification. The counterpart experimental method of anchoring concrete component with pre-buried loading devices can be used to test the relaxation behavior of anchoring structures. Furthermore, the fiber optic grating technology is employed to monitor the continuous long-term strain process of rod body. The measured strain data are accurate and stable.