A novel method for measuring the cutoff wavelength of waveguides with arbitrar y complex cross sections is proposed in this paper. Based on the theory of waveguide reson ant cavity, the measurement of complex waveguides is simplified into that of resonant cavities. Consequently, the difficulties of matching and transition are excluded, and high accuracy is also obtained.This measurement method is regarded as a better choice in microwave engineering desig n. The measurement methods for waveguide attenuation and field distribution are also in cluded．