Artificial intelligence (AI) and its application are developed explosively not only in control field but also in signal and information processing field. Fuzzy theory is an important branch of AI. In fuzzy enhancement theory of image processing, Pal function is often employed as the membership function. Although this function possesses good filtering effect, the fuzzy factors of the function are often empirical values, which results to different image enhancement effects when the input images are different, and details of the enhancement image are not clear, then bad enhancement effect always appears. In this paper, the fuzzy factors are considered as variables. At the same time, an evaluation function is constructed to evaluate the enhancement performance, and a suitable optimization algorithm is used to obtain the most optimum values of the fuzzy factors automatically. Simulation results show good performance of the improved method.