She tied for most wins with British singer Adele, who also earned three trophies for female pop artist, best album with smash hit "21" and top adult contemporary performer.
But Adele, who came into the awards show as the most-nominated singer with four nods, lost artist of the year to Swift, who seemed genuinely surprised by the upset victory.
"This is one of the craziest things that has ever happened to me," Swift said. "I have no idea what I'm supposed to say. I did not think this was going to happen."
Along with year's top artist, Swift claimed AMA trophies for favorite female country artist for the second straight year, and she nabbed best country album with her "Speak Now."
Adele, who is recovering from vocal cord surgery, was not on hand to accept her awards.
Rapper Nicki Minaj was the night's other big winner with two AMAs in the rap or hip-hop category: favorite artist and best album for her "Pink Friday."
Minaj opened the show singing her smash hit single "Super Bass" in a metallic outfit that had two large speakers on her bottom, and after winning best hip-hop album for "Pink Friday" was overcome with emotion.
"This one could actually make me cry," Minaj said onstage before wiping away tears. "I can't believe this is happening."
MANY AWARDS, MANY WINNERS
Elsewhere, the AMA awards were split among numerous acts.
The AMA awards is among the most widely watched of the annual U.S. musical honors at the end of each year. Next up on the list of key honors are Grammy nominations, which will be announced on November 30.