Abstract: In order to improve the quality of terahertz image and overcome the problem of edge blur of terahertz image, a super-resolution reconstruction method, which combines rational fractal interpolation and gradient field transform, was proposed in this paper for terahertz image reconstruction with frequencies of 0.25THz, 0.50THz, and 0.75THz. Meanwhile, spatial entropy-based image enhancement and bilateral filtering are introduced to optimize the reconstruction. Experimental results illustrate that after processing interpolated terahertz images by super-resolution reconstruction based on gradient field transform, the edge strength of images with frequencies of 0.25THz, 0.50THz, and 0.75THz were respectively improved by 169%, 116%, and 104%, and the average gradient of those images were improved by 16%, 28%, and 24%, respectively. Moreover, signal frequency and intensity would affect the performance of the reconstruction. This method can recover the detail information in terahertz images, sharpen edges of the object, improve the quality of terahertz images without ringing effect, and has practical value.