An image restoration method of 2D reconstructed-image of terahertz Gabor in-line digital holography was proposed with combination of Piecewise-contrast-stretching Transformation(PCST) and Patch-based Locally Optimal Wiener (PLOW) filter. The PCST and the PLOW algorithms were introduced, respectively, and the working flow of the combined PCST-PLOW algorithm was given. The denoising for a real 2.52 THz reconstructed-image of digital holography was executed, and each step of the image processing was compared. The effect of the PCST on the image enhancement was analysis, in which the starting point and the end point of the nodes were dependent on a histogram and an image average value. The results of treatment on the real terahertz reconstructed-image show that the global standard deviation of the denoising reconstructed-image of 40-frame averaged hologram rises from 0.184 9 to 0.307 4, and the ratio of the mean value to standard deviation rises from 1.720 8 to 2.268 8. These results demonstrate that the proposed method has suppressed image noise, while improving image contrast.