To improve the stability and accuracy of small target tracking in cluttering background, a new small target tracking method based on gradient Laplacian of Gaussian (LOG) operator was proposed. First, imaging model of small target in gradient image was presented. Second, the theory of scale space was used to design a new operator for target detection and tracking. Then, the property of scale invariant was analyzed and proved, and a tracking scheme based on the gradient LOG operator was proposed. Experimental results show that the gradient LOG operator is appropriate to describe small target in complex background, and the detection precision is in the level of sub-pixel. Furthermore, it is efficient and robust to noise.