A method and an apparatus for controlling a bit rate are provided to transmits high definition or resolution moving picture in real time by controlling a bit rate and preventing the occurrence of the overflow or underflow of a bit row storage buffer based on the prediction of the image property of a current frame. The similarity between one block group among block group including plural macro block in a current frame and a block group of a previous frame corresponding to at least one block group is calculated(510). If the similarity is larger than a critical value, a target bit of the current block group to which current macro block belongs is determined(520). The target bit of the current macro block is determined based on the target bit of the current group(530). The quantization coefficient of the current macro block is calculated by considering the target bit of the determined current macro block and the bit which is generated up to the previous macro block(540).
