Li moves from third to No. 2 in the rankings and is the first Chinese player to reach that high in singles. Peng goes from third to No. 1 in WTA doubles, another first for a Chinese player.
Li is 13-1 this year, winning titles at Shenzhen, China, and the Australian Open before a quarterfinal loss last week at Doha. She was assured of moving to No. 2, however, when Victoria Azarenka withdrew from the Doha event.
Peng is 9-1 in doubles matches, with wins at Pattaya City, Thailand (with Zhang Shuai) and, while teaming with Hsieh Su-Wei for the title at Qatar.
Azarenka's missing the Qatar Open because of injury cost her two places in the rankings, as she slips to fourth with Agnieszka Radwanska going from fourth to No. 3 in addition to Li's move to No. 2.
The ranking for Halep represents a career high. She beat Kerber in Sunday's final of the Qatar Total Open. It was her seventh WTA title, all of which have come since last June 15.
World No. 1 Serena Williams, a late wild-card entry, returns to the court at the Dubai Duty Free Tennis Championships. She missed the Qatar Open because of a back injury.
Adding her to the field gives Dubai seven Top 10 players, with Radwanska seeded second.
The WTA Top 10 listing player's name, home country and rankings points:
1. Serena Williams, United States, 12,380
2. Li Na, China, 6,690
3. Agnieszka Radwanska, Poland, 5,705
4. Victoria Azarenka, Belarus, 5,681
5. Maria Sharapova, Russia, 5,206
6. Petra Kvitova, Czech Republic, 4,710
7. Jelena Jankovic, Serbia, 4,535
8. Angelique Kerber, Germany, 4,490
9. Simona Halep, Romania, 4,435
10. Sara Errani, Italy, 4,390