The 29-year-old will return on loan after just one season in Spain, with no transfer fee announced.
Paulinho played 34 games and scored nine goals as Barcelona won La Liga last term, and started all five of Brazil's World Cup games in Russia.
He made 63 league appearances for Guangzhou Evergrande from 2015-2017.
Barcelona confirmed the deal on their website, adding that Guangzhou have an option to sign the former Tottenham man on a permanent deal.
A mainstay of Brazil boss Tite's side in Russia, Paulinho scored once in the 2-0 group-stage win over Serbia and played 73 minutes of their 2-1 quarter-final defeat by Belgium before being replaced by goalscorer Renato Augusto.
He joined Tottenham for £17m from Corinthians in 2013, before moving to China in 2015.