The former England captain, who will combine the job with playing for Paris Saint Germain, was met by a media scrum and thousands of fans at the start of his four-day visit.
Beckham will attend league matches in China and visit schools to promote the game at grassroots level.
"Thank you for an amazing welcome," the 37-year-old, speaking at one school in the capital, said. "I'm very happy to be here, I've always been welcomed with open arms.
"Football has been part of my life since I was very young so I'm very proud to be an ambassador and to help the development of the game here."
Chinese football is working to recover from a match-fixing scandal that has seen several top officials, players and referees jailed or banned.
Television viewing figures for foreign leagues far outnumber those for the tarnished domestic league, while the national side failed to qualify for next year's World Cup.