A new algorithm of video watermarking based on changed area is studied in this paper. We propose a method to located area which pixels change greatly from three successive frames of uncompressed video by using three-frame differencing. Then we choose the region where changes drastically to embed watermark by using the Quantization Modulation algorithm in DCT coefficients. In order to have a good performance on video quality and embed more information, we divided the binary watermark into two parts which obtain a logistic Arnold transform before being embedded. The experimental results indicates that the proposed scheme has a good performance to frame dropping, frame cropping, frame rating, Gaussian noising, MPEG2 compression, etc. and it has a advantage on little degrading the video quality.