The present invention discloses an online service system capable of predicting waiting time. The service system serves the users through a queuing mode and an electronic whiteboard mode. The queuing mode comprises a queuing-user counting unit for counting number of the user entering the queuing mode, a service channel counting unit for counting number of the service channels providing service, and a waiting-time prediction unit for predicting and showing the waiting time to the queuing users. Alternatively, the queuing users can search for related information from the database through a search engine. Once the service channel is available, the queuing user can exit from the queuing mode and request for service through the electronic whiteboard mode by transmitting audio/video, picture and character data. The present invention may further provide a performance evaluation mode for the system manager's reference.