Disclosed in the present invention are a failure notification method, detection apparatus, forwarding apparatus, system and data structure. The failure notification method comprises: detecting whether a failure occurs in the main path of Internet Protocol (IP) multicast tree forwarding paths which are established based upon Protocol Independent Multicast protocol; when a non-switch node in the main path detects that a failure occurs in the main path, obtaining the failure information, and encapsulating the failure information in a failure notification massage; transmitting the failure notification massage to a switch node in the main path. According to above technical solution, in the failure notification method disclosed in the embodiments of the present invention, when the non-switch node detects that a failure occurs in the main path of the IP multicast tree forwarding paths, a failure notification message is transmitted to the switch node in the main path. Compared with the prior art, when the non-switch node detects that a failure occurs in the main path of the IP multicast tree forwarding paths, there is no need to transmit failure notification messages to all nodes in the multicast network which the IP multicast tree belongs to, and therefore the number of invalid messages is reduced.