The 30-year-old, who is considered China's most successful football export, arrives on transfer-fee free two-year deal after City decided against renewing his contract after six years at the club.
Sheffield United manager Kevin Blackwell will be pleased that the five-match ban that Sun picked up while on international duty recently means he cannot compete for China's Olympic team at the Beijing Games, thus meaning that the Blades' first permanent signing of the summer will not be absent for the month of August.