Characteristics of photo-thermal effect and the functional relationship between the discharge intensity and the released heat are still unclear. In this work, the discharge intensity and the released heat of microwave-induced metal discharge were quantitatively measured using photo-voltage conversion and hydro-thermal exchange method, respectively. The mechanism of microwave-induced metal discharge was also discussed. The average discharge intensity obtained with three wires within 10 min was 44.6% higher than that obtained with one wire. The released heat increased from 67.81 kJ to 113.7 kJ when three wires were inserted instead of one wire. The rate of heat evolution changed by a step way with the decrease of discharge intensity. The electron enrichment on the metal tip causes a skin effect, and then the enhancement of electron enrichment forms Joule heat. After the stage, the electrons escape from the metal surface and cause the breakdown of the medium, forming the discharge.