An embodiment of a method for decoding large images performed by a processing unit, comprises the following steps. A compressed bit stream of a minimum code unit (MCU) of an image is acquired. The acquired bit stream is decoded by performing a first stage of a image decoding procedure to generate a temporary decoding result of the acquired bit stream. It is determined whether the MCU requires display. If so, the generated temporary decoding result is decoded by performing a second stage of the image decoding procedure to generate display data of the acquired bit stream. The temporary decoding result of the acquired bit stream is utilized to decode another MCU of the bit stream.