This paper expatiates on the principle, process and key technique of the enhancement algorithm based on fuzzy set theory. In the algorithm, the critical point gc is determined via the Otsu algorithm based on the two-dimensional histogram, and then the fuzzy set of an image is determined via the exponential function, and then the fuzzy set is transformed for enhancement via a recursive operator, and eventually the enhanced image is attained via an inverse transformation from the transformed fuzzy set. Acting as an application to the image of high-voltage transmission lines, the experimental results of not only the transformation of histogram equalization but also the expatiated algorithm are given. The experimental results show the latter is more efficient than the former. One of main characteristics in the expatiated algorithm is that gc is determined via the Otsu algorithm based on the two-dimensional histogram instead of the others.