A server backup method and a backup system using the server backup method are provided. The server backup method includes continuously collecting a plurality of dirty pages during a running operation and determining a backup start time point according to a quantity of the collected dirty pages. The server backup method also includes suspending the running operation according to the backup start time point and executing a backup snapshot operation to generate a data backup snapshot corresponding to the dirty pages, and executing a backup transmission operation to transmit the data backup snapshot.