Amnesty said that in the last year alone, thousands of petitioners, reformists and others were arrested as part of a government campaign to "clean up" Beijing before the games, which open August 8. It said many of those arrested have been sentenced to manual labor without trial.
Chinese human rights activists have been targeted elsewhere in the country as well, Amnesty said in its report.
It cited the case of Sichuan-based activist Huang Qi, who was formally arrested earlier this month on charges of possessing state secrets. The case, though, is believed to stem from his work helping the families of children killed in May's earthquake bring a legal case against local authorities, Amnesty said.
The organization said the games, touted by Chinese and Olympic officials alike as a way to help expand freedoms in the authoritarian country, have instead led the government to muzzle critics in hopes of presenting an image of harmony and stability to the outside world.
"By continuing to persecute and punish those who speak out for human rights, the Chinese authorities have lost sight of the promises they made when they were granted the games seven years ago," said Roseann Rife, a deputy director in Asia for the London-based group. "The Chinese authorities are tarnishing the legacy of the games."
An after-hours duty officer at China's Foreign Ministry had no immediate comment on the report, although the Chinese government routinely denies such allegations, saying it has promoted human rights by reforming the legal system and raising living standards of hundreds of millions of people.
In once recent shift, the government announced it was setting up special protest zones during the games.
The Amnesty report also took aim at China's suppressive media censorship, noting that some foreign journalists have been harassed by authorities. Learn how China monitors the Internet »
It also claimed the government had expanded its "re-education through labor" program under which security forces arrest people and sentence them to manual labor without trial.
Amnesty also accused the International Olympic Committee of showing a "reluctance" to pressure China publicly on its human rights record.
Messages left with IOC spokeswoman Giselle Davies asking for comment on the report were not immediately returned.Elsewhere in the report, Amnesty welcomed China's move last year to restore the Supreme People's Court's role in approving death sentences. But it criticized the government, which says the number of executions has declined, for withholding data on death penalty cases.