The dead tourist was named as Yuan Dingrong, 56, who drowned in Ao La at Koh Racha.
Mrs Yuan came to visit Phuket on November 18 with nine relatives. She was staying in a hotel in Kalim and was due to leave Phuket on Sunday (November 25).
After she had been underwater for about 10 minutes, her daughter Liao Yuanyuan, realising that there must be something wrong, called for people nearby to help.
Mrs Yuan was pulled out of the water and taken to The Racha hotel nearby. A doctor in the hotel attempted to revive her with CPR but was unsuccessful.
She was rushed by boat to Phuket International Hospital at around 1:30 pm, where she was pronounced dead. Her body is being kept at the hospital until arrangements can be made for her return to China.
Meanwhile, Joyoti Chavhan, 44, from India also got into trouble while snorkeling off Koh Racha. She was taken back to Phuket by speedboat and then to hospital, where she recovered quite quickly. She has since been released and returned to her hotel.