With the rapid development of the world wide web, the network monitoring systems need to be built within the network, but due to huge cost, when the network monitoring system is designed, all of the edges can not be monitored at one time. Instead only a limited number of network nodes can be chosen to monitor a small part of the edge, and later the deployment of a new network monitoring node is increased. Based on the online theory, the online vertex covering problem
is studied. A competitive algorithm is presented with a constant competitive ratio. The performance of the competitive ratio is better than the existed result.