The move follows McLaren's recruitment of 13-year-old American prodigy Ugo Ugochukwu earlier this year.
The acquisition of Cui makes for a five-strong Mercedes junior squad, alongside Andrea Kimi Antonelli, Paul Aron, Alex Powell and Frederik Vesti.
A product of the central Chinese city of Xi'an, Cui is racing for Argenti Motorsport in the OK Junior karting classes in various series.
“We're really excited to welcome Yuanpu Cui to the Mercedes family as the newest signing of our young driver programme,” said Mercedes driver development advisor Gwen Lagrue.
“We're proud to be helping young drivers from a diverse range of countries and backgrounds on their rise up the motorsport ladder.
“Yuanpu certainly caught our attention and has shown great promise during his karting career so far.
“He's the top karting talent from China and there hasn't been a Chinese F1 driver yet, so we're looking forward to seeing how Yuanpu progresses and helping him move up the racing ranks.”