The　terahertz　(THz)　imaging　is　an　advanced　technique　on　the　basis　of　the　unique　characteristics　of　terahertz　radiation.　Due　to　its　noncontact,　non-invasive　and　high-resolution　capabilities,　it　has　already　shown　great　application　prospects　in　biomedical　observation,　sample　measurement,　and　quality　control.　The　continuous-wave　terahertz　in-line　digital　holography　is　a　combination　of　terahertz　technology　and　in-line　digital　holography　of　which　the　source　is　a　continuous-wave　terahertz　laser.　Over　the　past　decade,　many　researchers　used　different　terahertz　sources　and　detectors　to　undertake　experiments.　In　this　paper,　the　pre-process　of　the　hologram　is　accomplished　after　the　holograms＇　recording　process　because　of　the　negative　pixels　in　the　pyroelectric　detector　and　the　air　vibration　caused　by　the　chopper　inside　the　camera.　To　improve　the　quality　of　images,　the　phase　retrieval　algorithm　is　applied　to　eliminate　the　twin　images.　In　the　experiment,　the　pin　which　terahertz　wave　can＇t　penetrate　and　the　TPX　slice　carved　letters　＂THz＂　are　chosen　for　the　samples.　The　amplitude　and　phase　images　of　samples　are　obtained　and　the　twin　image　and　noise　in　the　reconstructed　images　are　suppressed.　The　results　validate　the　feasibility　of　the　terahertz　in-line　digital　holographic　imaging　technique.　This　work　also　shows　the　terahertz　in-line　digital　holography　technique＇s　prospects　in　materials　science　and　biological　samples＇　detection.