A monitoring server receives the latest monitored data and corresponding monitoring time from monitoring devices connected to the server at a specified time interval. The monitoring server records monitored data of each monitoring item and the corresponding monitoring time to a pointed node of a device data list, and adds the monitored data and the corresponding monitoring time, which are recorded in the pointed node of the device data list, into a monitored data list. When a web server requests real-time monitored data, corresponding monitored data is read from the device data list and sent to the web server. When the web server requests historical monitored data of an designated period, corresponding monitored data of the designated period is read from the monitored data list and sent to the web server.