Abstract: Microwave-assisted concrete coarse aggregate recycling technology has attracted extensive attention from scholars at home and abroad due to its green, effective, and low aggregate damage recycling properties. A multi-mode microwave resonator and conventional muffle furnace were employed to heat the cylindrical concrete specimens with different energy inputs. The investigation was performed for the heating efficiency, macroscopic crack expansion, material failure mode, splitting tensile strength weakening laws, and the influence laws of heating parameters on energy consumption and on energy efficiency. In addition, the mechanism of tensile strength weakening of concrete under microwave irradiation was analyzed through the scanning electron microscopy (SEM) tests. The experimental results show that the microwave heating technology has higher heating efficiency and can effectively promote crack propagation along the mortar-aggregate interface and then weaken the concrete strength. The higher the microwave power, the higher the thermal efficiency of concrete, the greater strength loss of concrete, and the lower the energy consumption. However, the mortar-aggregate interface was still compact under conventional heating, with no visible cracks occurred, and the energy efficiency during heating process was only about 1%.