Reinforced concrete structures are the most widely used structural forms in the world. The premise of the joint work between steel and concrete is that they have good bonding properties. Through comprehensive application of acoustic emission technology and AC impedance spectroscopy technology, the bond performance of rebar-concrete with different fly ash replacement rates is studied. By introducing an equivalent circuit model and investigating the changes of the resistance and capacitance of the steel-concrete interface, the damage development is investigated; the damage history under different load levels was obtained by analyzing the acoustic emission experimental data. The results show that the proper use of fly ash can strength the bond performance of steel-concrete. AC impedance spectroscopy and acoustic emission technology can be used to quantitatively study the development of bond damage.