The invention relates to a public network multicast issuing tree matching method, comprising: group management router calculates each covering degree value of the current private network multicast group in each existing public network multicast issuing tree; judging whether there is a public network multicast issuing tree whose covering degree value is greater than covering degree threshold: if yes, judging whether there is a unique issuing tree with the maximum covering degree: if yes, selecting the public network multicast issuing tree; if not, judging whether there is a unique static issuing tree: if yes, selecting the static issuing tree; if not, judging whether there is a unique most-quoted issuing tree: if yes, selecting the issuing tree; if not, selecting the earliest built public network multicast issuing tree. And it also relates to a VPN multicast implementing method, selecting matched tree or newly building a tree. And it reduces bandwidth waste. |