Liu Gang left China with the help of international human rights groups and arrived in the US penniless but with political asylum, the New York- based group Human Rights in China reported yesterday.
In Washington, presidential spokesman Mike McCurry said Mr Liu entered the US under a Justice Department waiver that allows admittance for emergency or national interest cases.
Mr Liu served a six-year prison sentence for participation in the 1989 Tiananmen Square pro-democracy protest, earning the nickname "Iron Man" for his refusal to bend to prison rules.
Robin Munro of Human Rights Watch Asia called Mr Liu "a very brave man and indomitable fighter for democracy" who was "badly tortured and beaten and ill-treated" in prison.
China has almost no dissident community left, Mr Munro said.
Released in June, Mr Liu returned to his family's home in Liaoyuan, in north-eastern Jilin province, where police kept a tight watch on him.
They surrounded his house, followed him and made it impossible for him to get a job. Mr Liu earlier said that police crashed into taxis he was in, and searched, detained and robbed him.
"The police in Liaoyuan treated me very badly. I couldn't bear them," Mr Liu said. They also ordered him to report his thoughts to them once a week, not to leave his home town and not to talk to foreign reporters. Mr Liu refused.
Mr Liu left his family home after his stepmother suffered mental disturbances because of the stress of police harassment.
He went to Peking last month to file an appeal asking to be left alone. Mr Liu said police threatened to arrest him again unless he returned to his home town.
The Human Rights in China report said police would cause so much trouble for anyone Mr Liu stayed with that he would be forced to leave.
It also said authorities refused to assign him a job or give him a licence for a small business like a street stall, and warned employers not to hire him.