Feng Chongyi, a China studies academic at the University of Technology Sydney (UTS), was conducting interviews for a human rights project.
"I'm not scared of them. I did not do anything illegal," he said after he was finally allowed to leave Guangzhou.
Dr Feng is an Australian permanent resident but retains a Chinese passport.
He travelled to China a month ago and was first questioned in Kunming in south-western Yunnan province, before twice being barred from flights leaving Guangzhou.
"If they wanted to scare me they failed miserably," Dr Feng said, vowing to return to continue his work on the project, which is part-funded by the Australian government.
"In terms of rule of law and human rights, it's getting worse and worse. It's clear their control of Chinese citizens become harder and harder," Dr Feng said.
He said he was made to sign a statement promising not to discuss his interrogation.
Supporters welcomed him back at Sydney airport on Sunday morning.