On iPhone, we can use iBeacon to wake up the APP in the background for Bluetooth scanning connection, now we want to port the function to AppleWatch APP, but the API related to iBeacon is not applicable on watchOS, does watchOS have a similar wake up mechanism?
The APIs needed for detecting iBeacons are not available on watchOS. If your beacon devices are able to advertise as a generic BLE device, you can use CoreBluetooth to wake up your watch app (albeit in a limited fashion).
You can find information about how that works on watchOS from Get timely alerts from Bluetooth devices on watchOS
and the related sample code Interacting with Bluetooth peripherals during background app refresh