A no-reference video quality assessment method is proposed for H.264／AVC network videos. The affection of packet loss on video qualities is first analyzed. Then, the video qualities are assessed by analyzing the spatial-temporal error propagation and error concealment which is induced by the new coding features of H.264／AVC. The complexity of the proposed quality assessment method is low, and it is suitable for assessing qualities of real time videos. Experimental results demonstrate that the MSE(mean square error) of the assessed video qualities is consistent with that obtained by full reference quality assessment. The correlation coefficient is greater than 0.85.