Abstract: Validation is an essential problem of XML documents. An active XML（AXML for short） document is an XML document where some of the data is given explicitly while other parts are defined intentionally by means of embedded calls to Web services. Informally, an AXML document can be seen as a set of XML documents. AXML documents greatly enhance the dynamic and flexibility of XML documents, but at the same time, they bring the new challenge of existing methods for checking validation of documents. This paper focuses on the problem of AXML documents validation. More precisely, a new tree automaton, AXML schema tree automaton （ASTA） is defined, which can efficiently represent the set of AXML documents conforming to the given schema. Based on ASTA automaton, an algorithm is proposed for checking AXML validation performing in polynomial time. The algorithm consists two parts: one is to check the validation of the current state of AXML document which means the document can be seen as a regular XML document and the other is to check the equivalent of the specification definitions of Web services. To test the efficiency of the algorithm, the algorithm is performed and the experimental results show that this algorithm gives rise to an efficient validation method for AXML documents.