Diffusion-based inpainting is a common method of small-area image tampering, considering the blurring effect introduced by diffusion-based image inpainting, this paper proposes a method of diffusion-based image inpainting forensics via gradient domain guided filtering enhancement. Since the texture of the forged image is clear in the untouched regions, and the blurring effect results in some texture changes in the inpainted regions, gradient domain guided filtering can better preserve the texture structure of the untouched regions and highlight the blurring effect of the inpainted regions. In view of the fact that the tampered information is reflected to different extend in different color channels, the gradient domain guided filtering is applied to enhance each color channel of the input image, which captures the impact of image inpainting from multiple perspectives. Experimental results show that this method can not only detect and locate the diffusion-based image inpainting regions effectively, but also has better detection performance than the existing methods.