Will i be able to pair an iPhone 7 Plus with an Apple Watch Series 8?

It appears not:

Set up your Apple Watch - Apple Support

To set up and use a new Apple Watch, you need an iPhone 8 or later with iOS 16 or later.

Here is what Apple says:

What you need

To set up and use a new Apple Watch, you need an iPhone 8 or later with iOS 16 or later. Learn how to identify your iPhone model and how to update your iPhone to the latest version of iOS.

If you think this information is wrong, you can proceed with your attempt to pair the watch to the iPhone 7. Good luck.

niroshmal wrote:

Apple Watch series 8can pair with Apple 7 plus phone

No, it can't.

Not sure if you understand that iOS 16 cannot be installed on an iPhone 7.

niroshmal wrote:

Apple Watch series 8can pair with Apple 7 plus phone

No.