The coupling mechanism between wave absorption and microwave metal discharges is very important in the application of microwave heating for the treatment of waste electronic scraps, tires, and other refuse of a similar nature. In this work, microwave absorbing material, metal strips, and their mixture embedded in quartz sands were irradiated by microwaves and an indirect calorimetric method was used to measure their heating effect to explore their coupling mechanism. Numerical study was also carried out to validate the experimental results and explain the mechanism in theory. The results indicate that the amount of microwave absorber directly influences the stimulation and the intensity of microwave metal discharges. An appropriate amount of microwave absorber is advisable for an efficient heating process by microwaves. The coupling mechanism of wave absorption and microwave metal discharges varies from collaborative to competitive with the increased amount of microwave absorber. Overuse of microwave absorber can counteract the improvement of microwave energy efficiency.