NGO worker Lee Ming-cheh went missing during a visit to the mainland in March and Chinese authorities later confirmed he was being investigated for suspected activities "endangering national security".
Lee's wife Lee Ching-yu said she had received a call from a man claiming to be her husband's lawyer yesterday telling her his trial was imminent.
China's Taiwan Affairs Office confirmed there would be a trial in Yueyang city in China's southern Hunan province, without specifying a date, according to local media.
Relations between the two sides have deteriorated since President Tsai Ing-wen took office in May last year and Beijing has cut off all official communication with Taipei.
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China sees self-ruled Taiwan as part of its territory to be reunified and wants Tsai to acknowledge the island is part of "One China", which she has refused to do.
Lee Ching-yu said in a statement that the man who called her asked her to go to China immediately because her husband's trial was about to start.
Despite the likelihood he would soon be jailed, Lee said she considered the possibility of seeing her husband "a ray of hope" and would apply for travel documents Thursday.
She attempted to fly to Beijing in April in a bid to "rescue" her husband, but Chinese authorities revoked her travel permit, preventing her from making the trip.
Taiwan's Mainland Affairs Council yesterday urged China to give Lee the necessary travel documents and to guarantee her personal safety.
"The actions so far by the mainland have only continued to deepen the suspicion Taiwanese people have towards China," it said in a statement.
She was planning to meet with the United Nations Human Rights Commission this month in Geneva.
In May she also testified at a congressional hearing in the United States on detained activists in China.