This paper proposes a novel multicast reliability algorithm in distributed virtual environment. Firstly, architecture of the distributed virtual environment system is made up of three layers, which are 1) Layer 1 is made up of distributed virtual environment server, which can transmit information from internet to clients, 2) Layer 2 is constructed by clients, which are connected to a specific server and can only solve a specific task, and 3) Layer 3 are tasks which should be solved by the distributed virtual environment system. Afterwards, the multicast problem of distributed virtual environment can be converted into a tree network with several nodes, of which the key issue is how to obtain a multicast strategy with the maximum reliability satisfying several constraints. Then, a multicast reliability algorithm for the distributed virtual environment system is present by finding key nodes and key paths in the tree network. Finally, experiments are conducted by both the performance evaluation metric “average cost” and “blocking probability” to demonstrate the effectiveness of the proposed algorithm