In order to set up a new effective method for measuring mechanical properties of the wood-plastics structural plates with stiffener, three different nondestructive testing (NDT) methods were used on the specimens with stiffener, which were made of virgin high-density polyethylene (HDPE) with poplar fibers as filler. The values of dynamic Young’s modulus of the specimens were measured by a FFT system. And the values of static bending modulus of elasticity (MOE) were also determined by three point bending test according to ASTM D790-03. The paper analyzed the variability of the dynamic Young’s modulus of specimens with stiffener obtained with different NDT methods, and the correlativity was also estimated between the dynamic Young’s modulus and the static MOE of all specimens. The results suggested that the intensity of the wood-plastics structural plates could be enhanced by stiffener, and the NDT methods could be appropriate to estimate the dynamic Young’s modulus of the wood-plastics structural plates with stiffener.