Abstract: Normalization design of XML database schema is to produce a set of XML schemas or DTDs that can well represent data dependencies and eliminate redundancies In the current researches on normalization design of XML database schema, data dependencies and redundancies in XML database schema are not analyzed specially The concept for identifiers is introduced to represent elements and attributes respectively, and redundancies in XML database schema structure: partial redundancies, transitive redundancies and anomalies, are analyzed Based on this, XML database schema in third normal form （3NF） is defined, and its normalization design algorithm is presented and proved