XPath becomes the basic mechanism for XML query. The non-deterministic operators in XPath, such as ‘//’ denoting ancestor-descendant relationship and ‘*’ denoting wildcards in XPath, greatly enhance the flexibility of XPath, but at the same time, introduce the complexity in XPath evaluation. How to explore DTD to reduce non-deterministic operators in XPath in order to improve the efficiency of XPath processing becomes a fundamental problem. The existing work focus on the limited fragment of XPath or DTD. This paper employs tree automata to express XPath and DTD in a unified framework, proposes a novel production operation on tree automata for XPath and tree automata for DTD, proves that the result of production equals to the optimized form of XPath in the presence of DTD, and generates the optimized XPath in a polynomial time based on the generation cost. The experimental result demonstrate that logical optimization on XPath can lead to the increase of efficiency on the existing XPath evaluator.