Disclosed is a method for data synchronization and update conflict resolution between mobile clients and a server in a mobile system which maintains consistency of data between the clients and the server and enables the clients to continuously perform an effective update operation with respect to objects of the server even in a clients' disconnection state by the mobile clients performing an independent update operation with respect to disjoint fragments and associated objects for a specified object using the structure of the objects and the meaning of applications and then performing the data synchronization and the conflict resolution between the clients and the server during a reconnection operation. The method includes a copy management step of copying data of a server-side DB into a client-side built-in DB and the server managing contents of copying and a copying time, a data synchronization step of synchronizing changed data between the mobile clients and the DB server with respect to a data change produced during the mobile clients' disconnection state in accordance with a request of the mobile clients after a reconnection of the mobile clients, and a conflict detection and resolution step of detecting an error that damages consistency of the data in the data synchronization process and resolving the detected error.