The invention discloses a method and device for generating an HDR image. The method comprises the steps: acquiring the brightness of an LDR image; obtaining the average brightness of the LDR image andthe weighted filtering brightness of the LDR image according to the brightness of the LDR image; obtaining an adjustment parameter according to the average brightness of the LDR image and the weighted filtering brightness of the LDR image; obtaining the extended brightness of the LDR image according to the average brightness of the LDR image, the brightness of the LDR image and the adjustment parameters; performing linear filtering on the extended brightness of the LDR image to obtain the filtered brightness of the LDR image; and combining the filtering brightness of the LDR image with the chromaticity of the LDR image to generate an HDR image. According to the technical scheme, the brightness level and the dynamic range of the LDR image can be expanded by utilizing the average brightness, the brightness and the adjustment parameters of the LDR image, and filtering processing is performed on the expanded image brightness so that detail information of the image can be enhanced and noise can be effectively suppressed.