Abstract: Histogram of differential frame （HOD） was introduced to allocate bits on frame level since it could indicate the motion degree of a picture effectively.Based on HOD pre-analysis,a frame-layer bits allocation scheme is proposed to replace the one used in AVC.In the scheme,a new model of sectional constant frame-layer bits allocation is proposed when motion distribution in a sequence is continuous.Otherwise,a revised linear HOD model is used to allocate bits for a frame if there is abrupt motion change.The final simulation shows that compared to H.264JM76,the proposed bits allocation scheme improves R-D performance by 0.35dB on average and manifests a more smooth subjective quality degradation.