Abstract: Media synchronization puts forward determinate requirements on end-to-end delay and delay jitter. The jitter buffers at the destination site can eliminate the effect of the delay jitter but increase the end-to-end delay. Then, the requirements of media synchronization guarantee on the network delay are not clear. From the point of view of statistical guarantee, this paper determines the range of the jitter buffer size for guaranteeing media synchronization, provides the sufficient condition for the network to guarantee the media synchronization, presents an synchronization guarantee evaluating examples with the sufficient condition and validates the sufficient condition by the actual network testing results on VoIP(Voice over IP) based on Internet.