Automatic exposure control is a process of optimizing image brightness by controlling the exposure. To achieve auto exposure in digital cameras, image brightness is widely used because of its direct relationship with exposure value. Although entropy has been used in various image processing applications, it has not been used for AE application. A new auto-exposure algorithm was proposed based on the image entropy. The proposed method calculated the entropy of captured images to estimate lighting conditions. By comparing the image entropy and entropy threshold, the images were divided into the regions of interest and regions of no interest. After that, assign different weights to the regions of interest and regions of no interest, so that the overall brightness level was made to carry more information of the regions of interest. At last, the image can get accurate automatic exposure. The algorithm is mainly based on the image entropy, so the exposures are not affected by the location of objects in the image. It can make the algorithm more flexible. The experiment results show that the algorithm can accurately detect high-contrast lighting conditions and improve the dynamic range of output images for a camera system, at the same time the algorithm can also increases the accuracy of auto exposure.