I finish a run just now,when I want to release it ,the website told me"Emulators are banned."

I don't use English as my main language,I can't understand what that meaning,please who can tell me what happend or I do anything wrong?

That just means you can't submit an Undertale run performed on a console emulator. It's not a warning, just a note on why the emulator option isn't available. If you didn't use an emulator then your run is fine to submit.