Abstract: With the development of research on XML database management systems （XML DBMS）,concurrent processing on mass XML data makes it very important to study the concurrency control protocols based on tree-structured XML data. The tree locking protocol,introduced by Silberschatz and Kedem,was defined based on static tree-structured data. However,as is known,XML data items are the dynamically changing tree-structured data. In accordance with the properties of XML data,a set of operations are defined,which can be used to change XML document from one tree-structured form to another legal tree-structured form. The most distinguished feature of this set of operations is that its operating object is a subtree,not a single node of the XML document. This characteristic fits for the XML data very much,because the valuable information of XML document tree all lies in its leaves. Based on this set of operations,an XML dynamic tree protocol （XDTP） is presented and it is proved that this protocol,just like its static counterpart-tree protocol,continues to ensure serializability and deadlock-freedom in the presence of these operations. Experiments are conducted on the DBLP XML data set. The results of these experiments demonstrate that the XML dynamic tree protocol XDTP performs very well in this circumstance.