Bryan Shepherd, 49, is accused of molesting the teen beginning when she was 13. Shepherd is a former track and girls basketball coach at Bellflower High School.
Shepherd pleaded no contest to one count of continuous sexual abuse of a child and two counts of forcible lewd acts on a child.
The prosecutor said Shepherd would received 28 years in state prison under terms of a negotiated settlement. Shepherd's sentencing is scheduled for March 25.
Although Shepherd was a high school coach, authorities said the crimes did not occur at the school. The victim was molested from the time she was 13 in 2005 until she was 17 in 2010, according to authorities.