The tourist, whose name has not been revealed, was swimming near Koh 7 in Mu Koh Similan National Park on Saturday when he showed signs of drowning, said officials from Thai Maritime Enforcement Center Region as cited by Bangkok Post.
Rescue forces quickly brought him to shore and gave first aid before sending the man to a nearby hospital.
However, he was pronounced dead later by doctors, The Phuket News reported.
The Similan Islands form an archipelago of 11 islands in the Andaman Sea, just 120 km northwest of Phuket island.
The area is famous for its pristine beaches with clear blue waters that attract thousands of tourists every year.
Thailand received 3.51 million Chinese tourists last year, missing its five-million target.
This year, it eyes 8 million Chinese arrivals.