Williams, who won the first China Open title in 2004, came away a 6-2, 6-2 winner over Jankovic in their fourth career meeting in a championship match.
Sunday's match opened with a pair of long games but Williams won both and then went up 3-0 by holding at love. She finished the set with her second break.
Jankovic picked up a break by winning a 17-point game for a 2-1 lead in the second set but Williams answered by winning five straight games, finishing the tournament with her fifth break on her third match point.
Williams, with 10 wins this year, has 56 WTA championships in her career, which is fourth most. She has a way to go to reach the top three however, as Steffi Graf, who is third, won 107 times on the tour. Martina Navratilova holds the record with 167 wins and Chris Evert is second with 157.
Jankovic, who is 4-7 all-time versus Williams, is 13-18 in WTA title matches. She also finished second to Williams in South Carolina earlier this year and twice in 2008, including at the U.S. Open.
Williams earned $860,000 along with the China Open championship, giving her career winnings of more than $51 million. That is far and away the WTA record; Venus Williams is second on the list at about $29 million. Jankovic's career winnings top $15 million after her $430,000 payday as the China Open runner-up.