Geng He, wife of Gao Zhisheng, said the three made a harrowing eight-day trip by motorcycle from southern China across the mountains of Southeast Asia to Thailand in January.
Granted refugee status by the United Nations in Bangkok and asylum by Washington, the family flew to the United States on Tuesday without Gao, she said.
He disappeared early last month and is believed to be in police detention. Geng said she did not know where her husband was and feared for his safety.
"We left because of the Chinese Communist Party's long-term persecution of my husband and the close surveillance and crackdown on our family," Geng said in a telephone interview from Arizona.
A self-trained lawyer, Gao began drawing scrutiny after taking on several politically charged cases, including persecution of members of the banned Falun Gong spiritual movement. He later began to advocate constitutional reform of the authoritarian government.
For more than three years, the family has been under constant watch by plainclothes and uniformed police in Beijing. Last year authorities barred their 15-year-old daughter from going to school, leaving her depressed and suicidal, Geng said.
Geng said she, their daughter and 5-year-old son managed to leave Beijing for the southwestern border province of Yunnan on Jan. 9. She said her husband was not in Beijing when they left.
She said she paid the traffickers, known by Chinese as snakeheads, 40,000 yuan ($5,850) to smuggle her and the children by motorcycle. The smugglers, who barely spoke Chinese, insisted at one point on splitting up the family to evade capture. For nine hours, she said, she was separated from her son and did not know if they would be reunited.
"The whole way, I didn't know where we were or how much longer we would be traveling," she said. "We were so scared."
Officials at the U.N. High Commissioner for Refugees in Geneva and the U.S. Embassy in Beijing said they could not comment on individual refugee cases.
Gao, 44, is one of the best known of a group of activist lawyers advocating legal reform and protections for human rights. He was nominated for a Nobel Peace Prize last year along with political dissident Hu Jia.
Judicial authorities revoked Gao's lawyer's license three years ago. He was arrested in August 2006 on subversion charges based on nine articles posted on Web sites abroad, the official Xinhua News Agency reported then. He was convicted and later placed under house arrest.
In a memoir published last year and in earlier open letters, Gao denounced China's human rights situation and detailed his and his family's harsh treatment by security forces.
He described torture sessions he said he endured that involved severe beatings, electric shocks to his genitals, and cigarettes held to his eyes.