The terahertz(THz) imaging system with a backward wave oscillator(BWO) is a new approach to nondestructive testing. The sample is placed on an [EQUATION]-[EQUATION] two-dimensional stage controlled by a computer. The intensity information of the terahertz wave after passing sample is collected by a pyroelectric detector, and then it can image by the computer. A number of potential imaging applications are demonstrated using the 0.71 THz radiation, including nondestructive real-time testing for plastic bus fare card, campus debit card and various articles contained in an envelop. The spatial resolution ability of the system is measured to be 1.5 mm. And the digital image processing is presented based on the result of the imaging system. The conclusion indicates that the image results are more distinct, after the optimization, which can improve the ability of continuous wave imaging technology. The results reveal that the BWO THz imaging system is very practical and effective in nondestructive identification and security inspections applications in future.