  This paper describes NiuTrans neural machine translation systems of the WMT
2021 news translation tasks. We made submissions to 9 language directions,
including English$\leftrightarrow$$\{$Chinese, Japanese, Russian, Icelandic$\}$
and English$\rightarrow$Hausa tasks. Our primary systems are built on several
effective variants of Transformer, e.g., Transformer-DLCL, ODE-Transformer. We
also utilize back-translation, knowledge distillation, post-ensemble, and
iterative fine-tuning techniques to enhance the model performance further.
