"It's a really urgent situation... it's going to last for a very long time and it needs global effort from different nations," said Ai, on his first return to London for five years.
"I think Western countries have to... help each other and get a better, more sound way to deal with the situation," added the 58-year-old, revealing that he was preparing a work on the plight of refugees.
His plea comes on the day that more than 100 British cultural figures, including actors Benedict Cumberbatch and Keira Knightley, signed a statement calling for the Conservative government to take in more asylum seekers.
The artist, who was handed back his passport in July, four years after it was confiscated, said he was "very proud" of the "civilised" welcome Germany -- where his son lives -- had given refugees.
The German authorities anticipate the arrival of 800,000 asylum seekers this year, equivalent to one percent of its population.
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Ai has a strong relationship with Germany, which was quick to issue him with a four-year multiple-entry visa after his passport was returned.
By contrast, Britain only recently ordered officials to grant the artist a six-month visa, reversing a decision to restrict him to a short trip that had prompted condemnation from rights groups.
The inability to travel for four years had "deeply affected" the artist, he said Friday.
"My son had nightmares that they would never let me out," he added.
Ai will now divide his time between Berlin, where he intends to teach, and Beijing, but warned that artists had to be "very careful" when working in China.
"There is always censorship and self-censorship there, unless you don't care and don't want to show there." he said.
His retrospective opens on September 19 and will run until December 13.