One fast inter mode decision algorithm is proposed in this paper. The whole algorithm is divided into two stages. In the pre-stage, by exploiting spatial and temporal information of encoded macrobocks (MBs), a skip mode early detection scheme is proposed. The homogeneity of current MB is also analyzed to filter out small inter modes in this stage. Secondly, during the block matching stage, a motion feature based inter mode decision scheme is introduced by analyzing the motion vector predictor's accuracy, the block overlapping situation and the smoothness of SAD (sum of absolute difference) value. Moreover, the rate distortion cost is checked in an early stage and we set some constraints to speed up the whole decision flow. Experiments show that our algorithm can achieve a speed up factor of up to 53.4% for sequences with different motion type. The overall bit increment and quality degradation is negligible compared with existing works.