THz array imaging system is constructed by utilizing the thermal imager of Pyrocam III made in USA and laser of SIFIR-50. Imaging experiments on 20 paper money with 2.52 THz laser are done in order to explore array imaging mechanism and method of imaging enhancement. The effects of the methods of contrast stretching transformation, histogram equalization, and median filter are studied according to the THz array image added by 5 images. The experimental results show that employing this imaging system and subsequent image processing, the images obtained are similar with the objects. For the low contrast images, the effects are not obvious only by contrast stretching transformation. Good effects are gained with the method of histogram equalization, and the effects of image enhancement are better when employing mean filtering after histogram equalization.