The Polish top seed was well worth the 6-3 6-4 win over her Chinese opponent and will face Dominika Cibulkova in Friday's final after the Slovakian stunned German second seed Angelique Kerber 6-2 4-6 6-3.
"I think I was really playing good tennis the last couple of days," said Radwanska, who also won the Auckland Classic last week and has started the year with eight straight wins. "I hope I can continue playing at this level."
Although Radwanska has had a busy schedule, Li was clearly tired after playing nine times in 10 days as well as managing to fit in a flight from China to Australia after winning last week's Shenzhen Open.
The Pole broke on Li's first service game and rarely looked back before stuttering to close out the match as she had in beating Yanina Wickmayer in Auckland last week.
"It was kind of like a deja vu from Auckland final," she said. "I'm really ready for the Australian Open. I will do of course everything to win that match tomorrow as well, and we'll see. I hope to win 16 matches in a row."
Cibulkova added world number five Kerber to her list of top 10 victims in Sydney this week having already beaten Petra Kvitova and Sara Errani.
Dominika Cibulkova (Slovakia) beat 2-Angelique Kerber (Germany) 6-2 4-6 6-3
1-Agnieszka Radwanska (Poland) beat 4-Li Na (China) 6-3 6-4
8-Sloane Stephens (US) beat Lauren Davis (US) 6-3 4-6 7-5
9-Mona Barthel (Germany) beat Tsvetana Pironkova (Bulgaria) 6-3 6-3
Elena Vesnina (Russia) beat Jarmila Gajdosova (Australia) 6-3 6-2
Kirsten Flipkens (Belgium) beat Monica Niculescu (Romania) 2-6 6-4 6-0