Real-time imaging is one important development direction of THz imaging technology. In this paper, utilizing CO2-pumped THz laser made by Coherent Inc. and 124 ×124 array detector, imaging experiments on RMB watermark are made and the experimental results are studied. In the experiments the frequency of the laser is 2.5 THz. The method of image averaging could realize the improvement of the image signal-to-noise ratio and the extraction of the watermark image is achieved by the method of the threshold segmentation. The real-time clear images of RMB watermark have been obtained from this imaging device and the image processing methods used could make the watermark clear. The experimental results show that this imaging mode has enormous advantage of improving image resolution and imaging frame.