it’s impossible to change account email address here https://addons.mozilla.org/en-US/firefox/users/edit
however, my email address is expiring and i don’t konw what to do 
You can create a new account with the new email address and then transfer your add-ons / collections to that account. The one thing you can’t do is transfer your reviews.
I’m a developer but original register email is not available anymore, how could I migrate original email to a new one? The most important thing I want is I can use new account to upload or manage my extension.
Please email amo-admins AT mozilla DOT org for help.