Ralkage If you're using Apache, you can create a rewrite rule to handle what you want to be done. Though I have only tested this with Vbulletin in the past, I can't really tell you how it'll behave with your Flarum installation.
If you use redirections, it works without problems. Flarum will never know, that your URLs have been redirected before. Put this into your .htaccess
file at the public html root level:
RewriteCond %{HTTP_HOST} ^twikor\.cn$ [NC]
RewriteRule ^discuss(.*)$ http://discuss.twikor.cn$1 [R=301,L]
Whether you could use silent rewrites as well, where both URLs deliver the same content without being changed from one into the other, I don't know. I would also advise against such an attempt, because Google doesn't like duplicate content.