An　organic　protective　coating　system　plays　an　important　role　for　the　corrosion　protection　of　offshore　metallic　structures.　It　is　of　practical　importance　to　detect　possible　coating　defects　and　evaluate　coating　performance　for　corrosion　degradation　monitoring.　Reliable　defect　identification　can　provide　timely　and　effective　maintenance　to　avoid　serious　consequences.　This　work　investigated　various　multilayer　organic　coating　systems　by　terahertz　pulse　imaging　technology　and　aimed　to　explore　the　inspection　ability　of　terahertz　non-destructive　testing　(THz　NDT)　of　protective　coatings.　Several　types　of　defective　coating　samples　were　measured.　The　comparison　of　measurements　obtained　for　sites　with　and　without　defects　was　provided.　The　changes　in　the　signals　caused　by　the　presence　of　defects　were　explained.　Structural　analysis,　quantitative　evaluation,　and　defect　identification　were　carried　out　in　detail.　The　results　of　measurements　showed　that　corrosion　defects,　paint　bulge　defects,　and　paint　detachment　defects　can　be　distinguished　and　identified　in　combination　with　the　causes　of　defects.　It　can　provide　effective　technical　guidance　for　terahertz　technology　to　be　gradually　extended　to　engineering　applications.