Video coding rate control method and video coding rate control system

The invention discloses a video coding rate control method and a video coding rate control system. The method comprises the steps of calculating a distributable bit T*R obtained by a corresponding segment according to the time length T of the segment and the average code rate R of code stream, respectively calculating coded I, B and P frames to obtain the rate R(Qi) of the frames or macro blocks, calculating inter-frame distortion according to the rate R(Qi), obtaining a quantization parameter Q corresponding to the minimum inter-frame distortion of a whole video sequence, and determining a distributed GOP bit according to the quantization parameter. The dynamic nature of video screen content within the time length of a segment is fully reflected, and the quality of video coding is improved.