Effective multicast congestion control mechanism is urgently needed with the deployment of multimedia multicast application in Internet. Layered multicast is considered to be an efficient approach to cope with the network heterogeneity. A Differentiated Services (DiffServ)-based layered multicast model is presented firstly. Then a congestion control algorithm for DiffServ-based layered multicast, called DSLMCC (DiffServ-based layered multicast packet dropping), including DSLMPM (DiffServ-based layered multicast packet marking) and DSLMPD (DiffServ-based layered multicast packet dropping) algorithm, is proposed through introducing probability-based priority packet marking and dropping mechanisms. Simulation results show that DSLMCC algorithm is more responsive, more stable and fair, and can adapt to network heterogeneity better.