A High Dynamic Range Image (HDRI) processing method is described, which multiple images of identical scene but with different exposure amount can be processed. The processing method is: A composite distribution, which is as target distribution of HDRI, is derived by pixel counts accumulation of the multiple original images. The accumulated distribution curve of target HDRI is then computed. To generate a composite image as original, a weighting method is used and the gray levels of pixels are calculated based on pixels in the multiple images. The tone distribution and the accumulative distribution curve are also obtained. Finally, using the accumulative distribution curve of the target image and of the composite image, a tone-converting curve is derived to transform the composite image to HDRI. The result shows that this method can make better use of gradation information of the original images. The tone range and the contrast of target image are extended.