State Attorney Willie Meggs made the announcement at a news conference, saying there was not enough evidence to win a conviction.
"After reviewing all the evidence in the case, we did not feel like we could meet that burden," Meggs said.
A search warrant from January, released hours before the news conference, detailed the woman's accusations for the first time. She told police she and friends had five to six shots at a bar and her "memory is very broken from that point forward." She said she remembered being in a cab with a "non-descript" black man and going into an apartment where she was raped.
The woman didn't identify Winston, who is black, until about a month after the alleged assault.
Winston, 19, has led the Seminoles to a No. 1 ranking and a shot at a national championship if they defeat Duke on Saturday.