The current Internet does not offer enough QoS (quality of service) guarantees or support to Internet multimedia applications. However, there are two requirements of multicast sending rate for Internet DTV at the server: 1) it can adapt well to the change of network congestion; 2) it can meet the rate requirement of programs. So multicast sending rate control is needed at the server. In this paper the difficulties of Internet DTV stream multicast are analyzed, and then a multicast rate control approach for network DTV stream based on buffer management is given. The algorithm can not only suit for the change of network traffic, but also satisfy the requirement of DTV decoder, by controlling the sending rate logically. The server first calculates the initial sending rate based on the timestamp included in the program streams and then detects the TCP-friendly bandwidth available. Finally taking the initial rate, the bandwidth available and the data occupancy ratio of send buffer into consideration together, a factual send rate can be got. The simulation results show that it can reduce the average packet loss ratio, increase the transmission quality of Internet DTV, and guarantees the sending buffer not to be overflowed, in comparison with the TFMCC method.