Abstract: Disclosed is a schema change method of a dual system capable of continuously providing service in dual system circumstances and simultaneously performing a schema change. The method preferably includes applying a changed schema to a standby system, connecting the standby system with an active system by a dual synchronous link, comparing schema versions of the systems, storing the data received from the database of the operating active system in the standby system, storing data received from a change buffer of the active system in the standby system, and performing a fail-over of the standby system and the active system.