The NiuTrans Machine Translation Systems for WMT20.

This paper describes NiuTrans neural machine translation systems of the WMT20 news translation tasks. We participated in Japanese English, English-\u003eChinese, Inuktitut-\u003eEnglish and Tamil-\u003eEnglish total five tasks and rank first in Japanese English both sides. We mainly utilized iterative back-translation, different depth and widen model architectures, iterative knowledge distillation and iterative fine-tuning. And we find that adequately widened and deepened the model simultaneously, the performance will significantly improve. Also, iterative fine-tuning strategy we implemented is effective during adapting domain. For Inuktitut-\u003eEnglish and Tamil-\u003eEnglish tasks, we built multilingual models separately and employed pretraining word embedding to obtain better performance.