Abstract: To apply microwave technology to rock fragmentation engineering as soon as possible, it is necessary to define the pattern of hard rock damage and constitutive relation with the microwave-force action. By introducing the D-P criteria and the Weibull distribution, a constitutive model of hard rocks with the microwave-force action is built, and through the microwave irradiation and uniaxial compression tests of hard granite, the pattern of microwave damage to hard rocks is explored and the constitutive model is verified. The study results show that the cracks in granite develop and the brittleness and strength are significantly reduced as the microwave power increases. At 4.0 kW,60% of the granite damage limit can be reached, and then the damage is not aggravated as power increases. Under the 1 min irradiation condition, the critical power of sample cracking is 3.33 kW and the critical power of melting is 5.33 kW. The unity coupling of the modified constitutive model is better, and especially for the section from the threshold value to the peak value, the coupling effect is extremely good, reflecting the conservatism with a high application value.