Microwave assisted TBM rock breaking is a new rock breaking technology with great potential to improve the rock breaking efficiency of hard rock tunnel. In order to study the microwave absorption capacity of rocks under normal and high temperature conditions, a set of variable temperature rock dielectric property testing system is designed based on the coaxial transmission/reflection method. The system is used to test three common rocks, basalt, sand stone and granite, during tunnel construction. The results show that the system can accurately measure the dielectric properties of rocks under variable temperature. The frequency has little effect on the dielectric properties of rocks, and the temperature has a certain effect on the dielectric properties of rocks. Imaginary part of dielectric constant of three kinds of rocks under normal and variable temperature ε″ and loss tangent tanθ. The relationship is basalt > sandstone > granite. The heating law of microwave heating of the three rocks is consistent with the law of dielectric properties. By testing the dielectric properties of the rock and analyzing the heating law, the microwave absorption capacity of the rock can be predicted in advance, and the microwave-assisted mechanical rock breaking can be selectively carried out for the tunnel with good microwave rock breaking effect.