The invention relates to the technical field of testing of material complex permittivity, in particular to a method for measuring material complex permittivity based on substrate integrated waveguide round resonant cavities. The method comprises the steps that firstly, the substrate integrated waveguide round resonant cavities with different resonant frequencies (work frequencies) are machined; secondly, for the substrate integrated waveguide round resonant cavities with the same resonant frequency, a sample with material identical to that of a dielectric layer 2, a standard sample with the known complex permittivity and a sample to be measured are respectively loaded, swept-frequency signals are fed respectively through a vector network analyzer, and the resonant frequencies and the quality factors of the three samples are tested; finally, simultaneous equations are established and solved, and then the complex permittivity of the sample to be measured at the work frequency of the corresponding substrate integrated waveguide round resonant cavity can be obtained. A multi-frequency-point clock test of the material complex permittivity can be completed in the mode that the substrate integrated waveguide round resonant cavities with other work frequencies are used and the same test process is repeated. The method for measuring material complex permittivity based on the substrate integrated waveguide round resonant cavities has the advantages that the sizes of the substrate integrated waveguide round resonant cavities are small, machining is convenient, and the precision of a measurement result is high.