Vibration intensity technique using cross-spectral density method was used to evaluate the quasi-longitudinal wave power in trapezoidal corrugated plates in the frequency domain. The established method for estimation of in-plane power in naturally orthotropic plates was used for measuring in-plane vibration power flow in trapezoidal corrugated plates. The aim of this work was also to determine the effectiveness of the method of 'elastic equivalence'. Measured in-plane power from corrugated plates was compared to that from isotropic plate. The effects of in-plane stiffness on vibration power were also investigated. It was necessary to remodel the trapezodal corrugated plates to rectangular corrugated plates so as to apply the method of elastic equivalence. In-plane power flow was observed to reduce gradually as the frequency increased. The effects of in-plane stiffness of the plate on quasi-longitudinal wave power flow were insignificant in the frequency range of interest. Some negative values of power were also observed in some frequency at the lower range.