There is no direct train from Beihai to Weizhou Island. If you want to take the bullet train to Weizhou Island, you can refer to the following steps:

1. You can take a bus or taxi from Beihai to Beihai Railway Station first.

Buy a train ticket to Nanning at Beihai Railway Station.

3. After arriving in Nanning, transfer to the bullet train bound for Beihai, and then get off at Beihai Station.

4. After arriving in Beihai, you can take a bus or taxi to the international passenger port, where you can buy a boat ticket to Weizhou Island.

The above information is for reference only. If you want to get to Weizhou Island more conveniently and quickly, you can choose to rent a car or charter a car to Weizhou Island in Beihai, which can avoid the inconvenience caused by multiple transfers.