Abstract: Terahertz waves can be used as a tool of non-destruction detection and imaging for certain kinds of materials because of unique characteristics. Improvement of imaging quality is of great significance to the application of terahertz imaging system. Digital image processing is a very important solution to the enhancement of imaging quality. Based on terahertz transmission imaging experiments, investigation was made on the use of image de-noising and enhancement techniques in order to suppress the influence of experimental noise of the imaging system and ultra-short laser power jitter. The methods included spatial domain filtering, Gaussian smoothing, frequency-domain filtering and edge detection. Analysis on the choice of methods and the comparison of effects was also given. Results show that, through an integrated use of image de-noising and enhancement techniques, the definition and identifiability of terahertz images are improved enormously.