To resolve the problem of high false alarm rate and low detection rate caused by the failure of existing background suppression algorithms in effectively suppressing complex backgrounds, a small target detection algorithm based on six-direction gradient difference anisotropic Gaussian filter suppression, double-layer orthogonal gray difference and diagonal gray difference target enhancement, and gray index adaptive threshold segmentation is proposed herein. First, a series of background suppression strategies are created using the Gaussian filtering technology and gradient difference concept. Then, the suppressed image is mapped on a double-layer sliding window using orthogonal gray difference and diagonal gray difference to enhance its local contrast as well as improve its target saliency. Finally, the real weak target is detected using the adaptive segmentation algorithm of the pixel gray index. Experimental results show that the background suppression factor index of the algorithm increases to 93%, and it can modify a background suppression model based on the local changes in the background to adaptively suppress prominent targets in complex backgrounds.