"大鹅" is the Chinese word for "swan," so you can say "swan" in Engpsh to refer to a large swan. Alternatively, you could use the scientific name for swans, which is Cygnus. Some examples of how you could use these words in a sentence include:
"I saw a beautiful swan swimming on the lake this morning."
"The swans at the park are so elegant and graceful."
"Have you ever seen a Cygnus up close? They are really impressive birds."