Outlook alias email address can’t show display name

What email services are you using? Is it in-house (exchange) or MS Office 365. Or another email services. How is Outlook connected to the servers?

how can I find out ? I am an end user.

Do you know how to navigate to Outlook / Accounts. If you can take a screen shot this will help me determine.

I saw it in the Account Setting, the type is Microsoft Exchange

If you open a new message from your main email account.  Click on Options/From in the message window.
This will add a "From" box in the message, clcik on the drop down arrow and either find or type in the alias.

Then send yourself the message.

If the message still appears to be from your main address then you don't have full "Send As" permissions for the alias.

Otherwise you should now be set up.  You just need to additionally remember who you are sending as(!)

thanks for your reply. what I mean is if other ppl click Check Name on out look using my alias email address, outlook cannot find my alias email in the active directory and display it as a name instead of alias email

In the Global Address Book (GAB)?
You expect both addresses to be listed if you search for your name or do you just want to appear as "Billy"?
Aliases are not usually listed to maintain integrity of the GAB structure.

both addresses can be appeared as Billy