A video encoding method and system are provided for encoding a video sequence. The video sequence includes N sub-sequences which each includes a plurality of frames. When the video encoding system encodes the jth frame in the ith sub-sequence of the video sequence, the frames previous to the jth frame in the ith sub-sequence have been encoded. Based on the encoded frames, an initial quantization scale is generated. According to the initial quantization scale, the jth frame of the ith sub-sequence is encoded in the inter-encoded mode. Whether the jth frame in the ith sub-sequence is a “scene change” relative to the (j−1)th frame in the ith subsequence is judged, and if YES, based on the initial quantization scale, an adjusted quantization scale is generated. Moreover, the jth frame in the ith sub-sequence is re-encoded in accordance with the adjusted quantization scale.