is apple watch 3 have SIM card?

Hi

The built-in cellular feature is only available on Apple Watch Series 3 (GPS + Cellular) models:

• Apple Watch - Compare - Apple
• Apple Watch Series 3 - Apple

Apple Watch Series 3 (GPS) models do not have SIM card (or any means of adding one) and can be used for calls and texts in the same way as previous Apple Watch models.

Apple Watch Series 3 (GPS + Cellular) models:

Have a built-in SIM / eSIM that copies information from the iPhone's SIM card.

Require a service plan from a supported carrier in your intended country of use that specifically includes support for the Apple Watch, including the carrier activating the device on the plan:

• Apple Watch - Carriers - Apple

Cannot use the built-in cellular feature when roaming.

Are not locked to any specific carrier, but there are three different regional versions of Apple Watch Series 3 (GPS + Cellular), each supporting different LTE and UMTS bands (see the previous link regarding carriers).

The SIM is built-in.

https://www.apple.com/watch/cellular/

Yes, it's an e-sim and is built-in, it's not the one you get from your carrier.