During recent years, the success of live swarm-based P2P streaming system has been witnessed. Nevertheless, how to design an effective mechanism for mitigating video quality degradation in a lossy network environment is still not thoroughly resolved yet. Unlike conventional client-server paradigm, there is data availability problem in swarm-based P2P streaming system. If we directly conduct the importance-first scheduling strategy in swarm-based P2P streaming system, the serious content bottleneck for low priority chunks occurs, particularly when the population size is large. In this work, we propose a dynamic strategy-switching approach that combines the advantages of random scheduling and importance first scheduling to deal with the problem. Simulation results indicate that our approach not only provides better scheduling efficiency, but also is scalable even if population size is large.