The invention discloses a noise reduction method and device for image noise. The noise reduction method comprises the following steps of 1) determining a block threshold value and a dynamic range of ablock gray scale of a macro block in an image according to an input decoded image; 2) obtaining a binary index of a pixel value in the macro block according to a comparison result of the pixel valueof a pixel in the macro block and the block threshold value of the macro block; 3) determining a pixel to be filtered in the macro block according to the binary index of the pixel value in the macro block; and 4) carrying out filtering processing on the pixel to be filtered by adopting a preset filtering algorithm. According to the method and the device, the noise reduction effect of mosquito noise is improved, and the image display after noise reduction is clear.