Prosecutors named him as Jian G in a statement on Tuesday and accused him of passing information about discussions in the European Union legislature to Chinese intelligence.
The website of Maximilian Krah, the AfD's top candidate in June's election to the assembly, lists Jian Guo as one of his assistants.
Krah said he had learned of Guo's arrest from the media and would stop working with him if the charges were proven.
Anxiety about alleged Chinese spying has mounted across Western Europe in recent months.
One of European parliamentarian Maximilian Krah's staffers has been accused of spying for China. (AP PHOTO)
On Monday, three German nationals were arrested on suspicion of handing over technology with military applications.
Two men were also charged in Britain on Monday with spying for China.
One of the men was reported to have worked as a parliamentary researcher for a prominent MP in the governing Conservative Party.
And on March 25, the US and Britain accused Beijing of cyber espionage against millions of people including MPs, academics and journalists, as well as companies such as defence contractors.
The aide, who lived in Brussels and the German city of Dresden, also spied on Chinese opposition figures in Germany, prosecutors said.
He was arrested in Dresden on Monday and his apartments were searched.
"He is accused of an especially severe case of working for a foreign secret service," the statement said.
The Czech newspaper Denik Na and the German magazine Der Spiegel reported earlier this month that another AfD candidate in the European Parliament election, German MP Petr Bystron, had received money from a pro-Russian media site.
The AfD said Bystron denied the allegation.
Konstantin von Notz, who heads the parliamentary committee supervising Germany's intelligence services, said these were not merely individual cases but pointed to a broader AfD problem.
"The AfD is a party of dictatorships," he said.
"They don't try to hide their contempt for our democracy and rule of law - and that clearly makes their politicians susceptible to being influenced and directed by China and Russia."
An AfD spokesperson said Monday's arrest was "very disturbing" and pledged the party would support the investigation.
Interior Minister Nancy Faeser said if the charges were proven, it was "an attack on European democracy from within", noting that Germany's security services had increased counter-espionage due to Russian hybrid threats and Chinese snooping.
In 2023, Krah had rejected allegations his aide was lobbying for China as slander against himself.
"It is about a staffer born in China," he wrote on the social media platform X.
"He is a German citizen, AfD member, studied in Dresden and speaks fluent German and English.
"There is a lot of lying going on."
The Chinese embassy did not immediately reply on Tuesday to requests for comment.
Foreign Ministry spokesman Wang Wenbin told a briefing reports of Chinese espionage in Europe were "hype" and "intended to discredit and suppress China".
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