Terahertz (THz) imaging has the advantages that THz radiation can penetrate most nonmetal and nonpolar materials for concealed objects detection, while it is harmless to the organisms. THz reflection-mode imaging has a more widely application range. Thus the penetrating ability for common packaging materials and clothes becomes very important to evaluate a THz reflection-mode imaging system. Therefore, penetration experiments are carried out by using a 2.52 THz reflection-mode scanning system. The system is constructed based on a CO2 pumped THz laser. The imaging targets are a razor blade, a penciled character, a 50 cents coin, a metal commemorative coin, and Siemens star. Papers, paper envelopes, and lab gowns are used as the shelters, and the imaging results are compared and analyzed. The experiment results demonstrate that the system can image through one layer of the lab gown or a paper envelope. The maximum insertion loss approaches 42 dB.