A method, server, user terminal, and system are disclosed for sending notification messages in the Internet communication filed. In the method: when detecting it needs to send a message to a target terminal, an application server detects a state of the signaling channel. When the signaling channel is in connected state, the application server sends a notification message to the target terminal through this signaling channel. When the signaling channel is in a disconnected state, the application server generates a notification request to a corresponding account of the target terminal and sends the notification request to the notification server so that the notification server pushes a notification message to the target terminal according to the notification request.