Based on the free-space method, a set of D-band transmittance measurement device is designed and developed, and typical clothes, shoes and wrappers are measured by the device. The device consists of a D-band vector network analyzer, two Gauss beam antennas, two hyperbolic lenses, an optical guide and a clamp. The through-reflect-line (TRL) calibration method and the time domain gate technique are adopted to improve the measurement accuracy and guarantee the validity of the data. Ten kinds of clothes with different thickness are measured by the device. The trend of data agrees with the published data well. Furthermore, three kinds of shoes and six kinds of wrappers are measured. The measured results are similar to those obtained by the security system, and are helpful to the design of security systems.