Abstract: The multi-source ALM(application layer multicast) can achieve multi-party interaction applications with less resources compared with the traditional multicast method. But the multicast characters, the application layer environment and the properties of the multi-source will make the congestion control of ALM worse. So a multi-source ALM congestion control method based on bi-directional pressure is proposed in this paper. By calculating the forward pressure and the backward pressure for every flow on local node, all the flows according to its weight share the local buffers so as to improve utilization. The forward pressure accelerates the data transmission speed and the backward pressure decreases the data volume produced by the source. To release the congestion on the local node and achieve the control target, the method limits the data volume of different flows in the local buffer. The ring congestion problem, which is critical for the multi-source ALM, has also been discussed in this paper, and a simple method has been proposed. PlanetLab experiment is given to demonstrate that the proposed method can be used to control the congestion effectively, balance flows and buffers of all the sources and achieve fairness and scalability.