This paper presents a terahertz (THz) wave reflection imaging system based on Backward Wave Oscillator (BWO). It is a new approach to non-destructive testing. The intensity information of the terahertz wave after being reflected from the sample surface or substrate is collected by a pyroelectric detector, and then imaged by computer. A number of potential imaging applications are demonstrated using the 0.7 THz radiation, including nondestructive testing for coins, badges, a model air-plane and some industrial samples that contain pre-built defects. This work reveals that THz radiation is highly transparent to many industrial materials, especially the “microwave-absorbing” material that is widely used in aero and space technologies