Yang Hengjun, 54, has been arrested but is yet to be formally charged, ambassador Cheng Jingye told reporters at a rare media conference in Canberra on Thursday.
“The relevant Chinese security department will deal with the case in accordance with Chinese law and his lawful rights are protected,” Cheng said.
Yang would be formally charged with espionage after an investigation, the ambassador said.
“In due time you will know the details,” he said.
He also said Yang’s wife Yuan Xiaoliang, who has been banned from leaving China, would be protected.
Foreign Minister Marise Payne has said Yang’s detention was “unacceptable.”
The pro-democracy campaigner is understood to be held in solitary confinement and shackled in chains, with restricted communications to family and friends.
Australia has previously asked for an explanation of the charges Yang is facing and requested he be given access to his lawyers.
But when asked on the conditions Yang was facing, Cheng said “the lawful rights of the person in question are well protected” and his health was “in good condition.”
“We expect the Australian side to respect China’s … judicial sovereignty,” he said.
Prime Minister Scott Morrison has said Yang’s treatment came to light during a recent visit by Australian consular staff.
“Australia always has to stand up for our citizens and we have to be true to who we are as a people,” he said earlier this month.
Yang was detained in January 2019 after flying into China from New York where he had been a visiting scholar at Columbia University
He’s a former official in the Ministry of Foreign Affairs in Beijing who went on to become a pro-democracy campaigner. He became an Australian citizen in 2002.
Yang and the Australian government deny the espionage allegations.
By Finbar O’Mallon