Herein, the aging and common defects of polyethylene (PE) pipe joints are inspected based on terahertz time-domain spectroscopy (THz-TDS). The reflective indices and absorption coefficients of PE specimens with different aging time are calculated,and the imaging detection for the typical defects of pipe joints is conducted. It is found that the reflective indices of the PE specimens have no obvious change in 0.2-2.0 THz range after aging for a long time. However, the absorption coefficient shows a decreasing tendency with increasing aging time. Finally, the defects are imaged using reflective THz-TDS. Pixels around the defect areas are different from those around non-defect areas in THz images, and the defect position and outline are revealed in the THz images.