Among the experiments of terahertz confocal scanning imaging, the image quality of the system remains to be improved for the reason that the terahertz laser used in the system can not constantly output and the signal acquisited by the detector is weak, etc. Digital image restoration is an effective method to save the cost and the space of confocal scanning imaging system. Based on the consideration above, a composite method was put forward for the use of the terahertz confocal scanning image restoration. This composite method is based on two-step background suppression, median non-local means(MNLM) filtering and gray level transformation. A comparison with median filtering, open operation and non-local means filtering was made after using this composite method on the real terahertz images. The results of real terahertz imaging processing show that this composite method has a good effect of image restoration and the image contrast is obviously enhanced in particular.