Vietnamese Treebank is a syntactically annotated corpus newly published in 2009. In this paper, we applied automated methods to detect errors in Vietnammese Treebank based on the concept of equivalence classes proposed by Dickinson. On this basis, we propose an improved method of error detection by transforming syntax trees based on vertical markovization. Our experimental results on Vietnamese Treebank showed that the scope of error detection was extended more than 2 times and the precision was improved more than 18.07% in comparison with the base line methods.