A critical problem for P2P streaming applications is to construct and maintain the overlay such that it continues to efficiently distribute data stream even in dynamic network environment. A common solution to this problem is to constantly adapt the overlay structure to the changing network conditions. However, in this paper, we propose an algorithm to schedule the sending order of queued data at each peer by taking into account both the data content as well as the overlay conditions. The data packets which are important to most users on the entire P2P system are sent out earlier. Simulation results show that the scheduling algorithm improves the overall streaming quality of the P2P system with little overhead added to the network traffic. Moreover, the improvement in overall streaming quality is also achieved regardless of the video streaming formats.