Can we integrate Elid Access Controller with Milestone Xprotect Access?

If you want to develop this integration, please start from this doc -

https://doc.developer.milestonesys.com/html/index.html?base=gettingstarted/intro_accesscontrol.html&tree=tree_4.html

so i need to develop a plugin first?

You are asking your question in the Developer Forum and therefore we might have assumed that you were asking because you wanted to develop a plugin.

Milestone Support will not always know if there is an integration already. Doing a search in marketplace came up empty: https://www.milestonesys.com/community/marketplace/start-exploring/?page=results&q=elid

There are integrations that are not announced in Marketplace, so I suggest you also ask the Access Control vendor. (I understand you are not the Access Control vendor.)