Terahertz　nondestructive　testing　is　an　increasingly　important　technology　in　recent　years.　Compared　with　visible　and　infrared　bands,　terahertz　wave　can　easily　penetrate　common　nonpolar　and　nonmetal　materials　without　ironize　the　sample　because　of　low　energy.　Digital　holography　can　reconstruct　the　quantitative　amplitude　and　phase　distributions　of　the　object　wavefront.　We　proposed　a　continuous-wave　terahertz　reflective　off-axis　digital　holography　to　measure　the　morphology　of　encapsulated　object.　An　experimental　system　was　built　using　a　2.52　THz　(118.83　mu　m)　far-infrared　gas　laser　295-FIR　and　a　pyroelectric　array　detector.　The　morphology　of　the　metallic　bookmark　hidden　behind　the　optically　opaque　materials　such　as　polytetrafluoroethylene　and　Polypropylene　plates　were　obtained　by　angular　spectrum　integral　and　phase　unwrapping　algorithm.　It　proves　that　THz　digital　holography　is　an　effective　nondestructive　testing　method.