Abstract: The scale space technique introduced by Witkin proposed an edge detection method by smoothing the image step by step. The smoothing process can be described as a traditional heat diffusion equation. In this paper it is assumed that heat diffuses from low temperature position to high temperature position and a new anisotropy reverse heat diffusion equation is obtained. This equation is used to design an image enhancement method （IEM ）, and through a suitable anisotropy function the gray value transfers from low gray value to high gray value mainly in the edges to be enhanced. The experiment results show that designing IEM through the new heat diffusion equation can make an efficient use of the conclusion of the scale-space technique, and a good enhancement result is obtained.