A webpage instant messaging system and method based on an HTTP protocol relates to the technical field of webpage instant messaging. The system including an active client end, an instant messaging server, a passive client end, a loop program and a clock program; the active client end sends a request through the instant messaging server and sends a message to the passive client end, and the messageis sent to the loop program; the passive client end receives the request and immediately feeds back to the active client end through the instant messaging server; the loop program is used to monitorwhether a change occurs in the message sent via the active client end, the clock program is used for recording a time period for which the message enters circular waiting and setting a maximum time length T for the circular waiting; when circular waiting time reaches T, the instant messaging server actively discontinues connection to the active client end, and the active client end resends the request after system shock is cleared. The application provides the webpage instant messaging system and method based on the HTTP protocol, and a small amount of server resource is occupied.