The invention discloses a micro controller unit (MCU) and a method for implementing multipicture split screen by using the MCU. In the method, the MCU determines source image sizes of sub-pictures in accordance with the split screen number and split screen mode of the multipicture split screen images; the MCU sends a command for adjusting image size to a conference terminal which participates in the multipicture split screen; the MCU receives video images which are coded based on the source image sizes, and the video images are sent by the conference terminal which participates in the multipicture split screen; the MCU splices images which are sent by the conference terminal which participates in the multipicture split screen into multipicture split screen images; and the MCU codes the multipicture split screen images and then sends the coded multipicture split screen images to the conference terminal. By using the method and the MCU, the terminal can adjust the sizes of the coded images which are sent to the MCU in accordance with the requirements of the MCU, thus reducing the sizes of decoded images required by the MCU, thereby decreasing occupancy of decoding resources on the MCU, and improving the multipicture split screen capacity of the MCU.