The present invention discloses a method and equipment for realizing three-layer multicast on-demand route selection based on PIM-SSM. When the interface is configured with corresponding on-demand path information, or the multicast join message carries on-demand path information, determine whether it is the device corresponding to the first hop in the on-demand path information link; if it is judged to be yes, According to the conventional multicast joining process, establish a multicast routing table entry, and forward the multicast joining message that does not carry the on-demand path information upstream; if the judgment is no, then establish a multicast routing table entry according to the on-demand path information , and forward the multicast join message carrying the on-demand path information to the device corresponding to the previous hop in the on-demand path information link. In the present invention, the flexibility of deploying the forwarding path of the multicast data flow is improved, and the manageability of the forwarding of the multicast data flow is enhanced.