An exposure control method and an image processing system are provided. The image processing system comprises: an image sensor module, configured to provide at least two types of source images in parallel, each type of the source images has different exposure setting; a pre-processing unit, configured to determine luminance distribution of the source images on block basis, perform a first exposure control according to the luminance distribution of the two types of source images, and generate output images according to the source images in RAW image domain, and a post-processing unit, configured to determine luminance distribution of the output images, and perform a second exposure control according to the luminance distribution of the output images in normal image domain; wherein exposure settings of the image sensor module is adjusted according to the first exposure control and the second exposure control.