The Intermediate People's Court of the city of Ningde ruled that Long Zhong, Zhu Zhenqin and Lin Guangshou were guilty of selling heroin, methamphetamine and ketamine from May 2011 to March 2012.
According to the court's order, Long will be executed immediately after the Supreme People's Court endorses his death sentence.
Zhu and Lin were sentenced to death with a two-year reprieve, state-run Xinhua news agency reported.
The defendants and their lawyers were not immediately available for comment.
The court upheld evidence showing that Long had supplied Zhu and Lin with 1.1 kilograms of heroin, 234 grams of methamphetamine and 9.5 kilograms of ketamine.