NiuTrans is a statistical machine translation system. It is free software and released under the terms of the GNU General Public License.It is developed by the Natural Language Processing Group at Northeastern University (China).It supports phrase-based, hierarchical phrase-based and syntax-based (string-to-tree, tree-to-string and tree-to-tree) models. The toolkit also includes a discriminative reordering model, a simple language model and a tuning tool using minimum error rate training.