China give Camacho birthday victory
Winger Feng Renliang was also on target for China, who returned to winning ways after their creditable 1-0 friendly loss to world champions Spain last Sunday.
Gao, who plays for Chinese Super League champions Guangzhou Evergrande, opened the scoring after nine minutes as he rose above the Vietnamese defence to head in Yu Hai's free-kick from the right.
The home side extended their lead in the 35th minute when former Celtic midfielder Zheng Zhi released Feng, who ran clear of the Vietnamese defence before coolly slotting the ball past goalkeeper Nguyen Manh Dung.
Gao emphasised China's dominance when he bagged his second of the game in the 63rd minute after meeting Sun Xiang's corner with a right-footed volley in the six-yard box.