High dynamic range (HDR) images are the images with HDR of lightness that can be recognized by human eyes, which can show more details about scenes. Aimed at one-exposure low dynamic range (LDR) images, we propose an HDR image generation method by fusing multi-level gamma-transformed images. The LDR image is firstly divided into four regions according to its histogram distribution. The Gamma parameter is calculated in each region based on the lightness level. Then, four images with richer details of different regions are generated by multi-level Gamma transform. Finally, they are fused into one HDR image with higher dynamic range and richer details. The tone-mapped HDR images generated by proposed method are compared with those by fusing multiple pseudo-exposure images. The results show that the proposed method has higher entropy and shorter running time.