The state-owned airline said in a statement the deal was part of its "strategy to invest in the strongest airlines around the world", but did not specify the cost of the transaction.
China Southern Airlines is one of China's "big three" carriers.
Qatar Airways also owns a 20 percent stake in International Airlines Group - which holds British Airways under its umbrella - as well as shares in LATAM Airlines Group, Italy's Meridiana and Hong Kong based Cathay Pacific.
The latest deal comes as Qatar seeks new partners and routes for the national airline due to an ongoing diplomatic dispute in the Gulf.
Since June 2017, Qatar has been politically and economically isolated regionally by Saudi Arabia, the United Arab Emirates and Bahrain.
These Gulf peers continue to impose a blockade, after accusing Doha of supporting "terrorists" and being too close to Saudi Arabia's Shia archrival Iran - charges Qatar denies.
The aviation deal follows warming relations between Doha and Beijing.
Government officials in Qatar said in November that China is now Doha's third largest trade partner, as bilateral exports and imports totalled more than $10 billion in 2017.
Qatar chose China Railway Construction Corporation to help build the $45 billion Lusail Stadium, an 80,000-seat arena that is meant to host the opening and final games of the 2022 World Cup finals.
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