Tossaporn Suksri, 27, and Pitakchai Wongsricha, 28, were found dead with broken necks, legs and arms in a bungee cage after its slings broke at 8.30pm on Friday.
Anupong Kantawong, 37, was injured and taken to Vachira Phuket Hospital.
All three worked for a company that was preparing to open a bungee-jumping attraction to the public.
The company had held a religious ceremony in the morning to mark the opening of the business. Afterward, it tested the system four times by putting sandbags weighing 75 kilogrammes into the cage and dropping it from the tower.
Mr Tossaporn, a partner in the business, and Mr Pitakchai, a maintenance staff member, then volunteered to test the cage. Mr Anupong agreed to test jumping from a tower.
The three went to the top of the 52-metre tower where Mr Anupong, with cords attached to his legs, prepared to jump into a nearby pool while Mr Tossaporn and Mr Pitakchai sat strapped into the cage.
After Mr Anupong jumped, the cage slid up and down on its slings a few times before they gave way, sending the car to the ground, killing Mr Tossaporn and Mr Pitakchai instantly.
Mr Anupong fell into the water and was slightly injured.
Police are investigating to determine the cause of the accident.
The accident revived memories of an incident involving a thrill ride at Santorini Park in Cha-am, Phetchaburi in July last year.
In the Santorini incident, a cord on the New Zealand-made G-Max Reverse Bungy snapped just before the ride was to launch. The three people in the cage were unhurt.
The Office of the Consumer Protection Board called for the regulation of amusement park rides after a video clip of the Santorini incident gained wide attention.
OCPB secretary-general Jirachai Moontongroi said at the time that Thailand had no specific laws to ensure that outdoor and indoor amusement machines and equipment are safe.
"We need more than just the Building Control Act, because many operators are now offering more amusement machines for play," said Mr Jirachai.
"It's easy for these operators, because they can just get permits from local administration organisations."
The operator of Santorini Park confirmed that in the absence of specific laws governing rides, it had sought a building and building modification licence from the local authority.
However, the company added: "The amusement machines and buildings at Santorini Park meet international standards."
The reverse bungee ride sends people into the air along guidewires, as opposed to the terrifying dive of a bungee jump.