Multimedia synchronization is the key technology in application of distributed multimedia. Solution of synchronization conflicts insides and among streams as well as that of user interaction, synchronization granularity refinement and synchronization precision improvement remain great challenges although great efforts have been invested by the academic circle. The construction method of a dual-scale dynamic synchronous model of multimedia presented in this article realizes multimedia synchronization on two scales based on two types of synchronous points, namely, natural synchronous points and pseudo-synchronous points, divided into two layers and taking the two methods of Petri net and agent. The model handles well with the relations of synchronization inside a stream and among streams, simplifies re-synchronization after real interaction with users and enhances dynamic synchronous expressive ability of multimedia.