您必须查询整个节点，而不仅仅是查询其内容：
pre = root.xpath('//gmd_identifier/gmd_RS_Identifier/gmd_pre/gco_CharacterString')然后，如果匹配，只需替换其文本并保存回XML文件即可：
if pre: # Replaces <gco_CharacterString> text pre[0].text = '{0328cb65-b564-495a-b17e-e49e04864ab7}' # Save back to the XML file etree.ElementTree(root).write('D:test.xml', pretty_print=True)就这样！:)
