A method for addressing a management object in a management tree of a device management (DM) client and an associated DM system are disclosed to solve the issues encountered in the relative universal resource identifier (URI) addressing of the OMA DM protocol. The method comprises receiving a relative URI including a first part from a DM server, and identifying a root node of the management object according to the first part. The first part comprises a URI parameter for specifying a root node of a sub-tree of the management tree for finding the management object, a management object identifier, and a plurality of attribute conditions for specifying values of a plurality of leaf nodes directly under the root node of the management object.