Abstract: Polyethylene (PE) structures, which poses a severe threat to structure integrity and would lead to structural failure. Therefore, it is imperative to detect and assess the buried defects in PE structures through effective nondestructive evaluation techniques. In this paper, microwave testing and imaging of the back-surface defect and inclusion in PE structures were intensively investigated. A direct-wave suppression algorithm based on singular value decomposition (SVD) was proposed for production of high-precision microwave images of defects. In parallel, two microwave probes i.e., the double-ridged waveguide and rectangular waveguide were compared in regard to quantitative evaluation of defects hidden within PE structures. The applicability as well as the superiority of the proposed signal feature of the microwave testing signal and SVD based direct-wave suppression algorithm for imaging and assessment of buried defects in PE structures was identified.