"I would like to ask people to go out and vote. This is another test for democracy and I hope we will pass this test."
About 400,000 military personnel are being used to persuade people to back the draft and the interior ministry has asked governors of all 76 provinces to order 80,000 village chiefs to get people to the polling booths.
Analysts say that for many Thais, the referendum is a vote on the coup of September 2006 that removed Thaksin Shinawatra, the twice-elected prime minister.
Ukrist Pathmanand, an analyst at Chulalongkorn University, said: "This is not about the constitution. It's about whether you accepted the coup or not. That's why the referendum is very important for the military."
The referendum requires a 50 per cent majority to pass a constitution which would take power from politicians and hand it to bureaucrats and judges.
It is designed to prevent the re-emergence of a single-party government such as Thaksin's.
Political analysts say the draft would take the country back to the 1980s when Prem Tinsulanonda, an ex-army chief, lead the country under a "managed democracy".
Prem is now chief royal adviser and is seen by Thaksin supporters as the mastermind of the coup.
After more than a year of political turmoil, some voters say that they are ready to approve even a flawed charter if it will ensure that elections are held soon.
A vote against the draft would leave power with the military. It would then pick one of Thailand's previous 17 constitutions, revise it and circulate it within 30 days.
Sonthi Boonyaratglin, the coup council chief, had said on Friday that if the draft charter is rejected, it would take him a couple of days to pick his favourite constitution.
"It would definitely take less than 30 days to promulgate another constitution," he said.
Polls open at 8am (0000 GMT) for eight hours of balloting at 87,000 stations catering for about 45 million voters.
A low turnout would be an embarrassment for the generals and, as in most Thai elections, allegations of vote buying have surfaced.
The military council and the government it had appointed are hoping to get at least 60 per cent of the ballots, arguing that the new charter would provide an "ethical" and "legitimate" democracy.
Awards will be given to the governors with the highest turnouts.