An in-situ operation, administration, and maintenance, iOAM, packet transmission method, wherein the method is applied to an iOAM network, the iOAM network comprises a measurement domain, the measurement domain comprises a tail node device, the tail node device is an egress device in the measurement domain, and the method comprises: receiving, by the tail node device, a first iOAM packet sent by a first node device, wherein the first iOAM packet comprises first node information and service data, the first node information indicates information about the first node device that transmits the first iOAM packet, and the measurement domain comprises the first node device; determining, by the tail node device, whether the first iOAM packet comprises an important data identifier, wherein the important data identifier indicates a node device in the measurement domain to trigger, in a process of transmitting the first iOAM packet, an important event that meets a predetermined condition; and when the tail node device determines that the first iOAM packet comprises the important data identifier, generating, by the tail node device, a notification message based on the first iOAM packet, and sending, by the tail node device, the notification message to a management device in the iOAM network, wherein the notification message comprises the first node information; wherein the notification message further comprises tail node information, and the tail node information indicates information about the tail node device that transmits the first iOAM packet; and wherein before the determining, by the tail node device, whether the first iOAM packet comprises an important data identifier, further comprising: detecting, by the tail node device, whether the tail node device triggers, in a process of transmitting the first iOAM packet, the important event that meets a predetermined condition comprising determining whether congestion occurs, and/or whether a packet transmission path changes; and when the tail node device determines that the tail node device triggers, in the process of transmitting the first iOAM packet, the important event that meets the predetermined condition, updating, by the tail node device, an important data identifier in the first iOAM packet; and wherein the important data identifier comprises a value that increases as a quantity of node devices that trigger the important event that meets the predetermined condition increases. receiving, by the tail node device, a first iOAM packet sent by a first node device, wherein the first iOAM packet comprises first node information and service data, the first node information indicates information about the first node device that transmits the first iOAM packet, and the measurement domain comprises the first node device; determining, by the tail node device, whether the first iOAM packet comprises an important data identifier, wherein the important data identifier indicates a node device in the measurement domain to trigger, in a process of transmitting the first iOAM packet, an important event that meets a predetermined condition; and when the tail node device determines that the first iOAM packet comprises the important data identifier, generating, by the tail node device, a notification message based on the first iOAM packet, and sending, by the tail node device, the notification message to a management device in the iOAM network, wherein the notification message comprises the first node information; wherein the notification message further comprises tail node information, and the tail node information indicates information about the tail node device that transmits the first iOAM packet; and wherein before the determining, by the tail node device, whether the first iOAM packet comprises an important data identifier, further comprising: detecting, by the tail node device, whether the tail node device triggers, in a process of transmitting the first iOAM packet, the important event that meets a predetermined condition comprising determining whether congestion occurs, and/or whether a packet transmission path changes; and when the tail node device determines that the tail node device triggers, in the process of transmitting the first iOAM packet, the important event that meets the predetermined condition, updating, by the tail node device, an important data identifier in the first iOAM packet; and wherein the important data identifier comprises a value that increases as a quantity of node devices that trigger the important event that meets the predetermined condition increases. detecting, by the tail node device, whether the tail node device triggers, in a process of transmitting the first iOAM packet, the important event that meets a predetermined condition comprising determining whether congestion occurs, and/or whether a packet transmission path changes; and when the tail node device determines that the tail node device triggers, in the process of transmitting the first iOAM packet, the important event that meets the predetermined condition, updating, by the tail node device, an important data identifier in the first iOAM packet; and wherein the important data identifier comprises a value that increases as a quantity of node devices that trigger the important event that meets the predetermined condition increases.