Mr Soros warned that artificial intelligence and machine learning could be used to entrench totalitarian control in the country.
He said this scenario presented an "unprecedented danger".
But he said the Chinese people were his "main source of hope".
"China is not the only authoritarian regime in the world but it is the wealthiest, strongest and technologically most advanced," he said, noting concerns too about Vladimir Putin's Russia.
'Security risk'
"This makes Xi Jinping the most dangerous opponent of open societies," he said.
Mr Soros, a prominent donor to the Democratic Party in the US, also criticised the Trump administration's stance towards China.
"Instead of waging a trade war with practically the whole world, the US should focus on China," he said.
He urged Washington to crack down on Chinese technology companies such as Huawei and ZTE, which he said present an "unacceptable security risk for the rest of the world".
More broadly, Mr Soros cautioned that repressive regimes could utilise technology to control their citizens, in what he called "a mortal threat to open societies".
