A dangerous sex offender who is already incarcerated has been sentenced to two years in prison for raping a teenage girl more than 13 years ago in Western Australia.

Harley Darren West pleaded guilty on the first day of his trial in March to sexually penetrating a 14-year-old girl in April 2001 when he was aged 35.

A trial was set at the time of the offence, but the victim was unwilling to testify so the case was dismissed, the Perth District Court heard on Friday.

Later, West was convicted of sexually abusing other girls and was charged again for the 2001 matter.

The victim's evidence was pre-recorded in October before West changed his plea.

In sentencing, Judge Philip McCann said the plea did not indicate remorse or empathy for the girl.

"Whilst it fell short of coercion, he only obtained the victim's consent by refusing to take no for an answer, which I find was aggravating," he said.

West, who was on parole at the time, had been armed with a machete but did not use it to threaten the girl, the court heard.

"It is relevant that the victim regards herself as having been raped," Judge McCann said.

In January 2013, West was deemed a dangerous sex offender and was detained subject to a continuing detention order.

He is currently part of the intensive sex offender treatment program.

By the end of June, West will have been incarcerated as a sentenced prisoner or a detainee under a CDO for 10 years.

The first annual review of his CDO was in March, but the court chose not to release him.

Judge McCann sentenced West to two years in prison and ordered that he be eligible for parole in May 2015, shortly after the next scheduled review of his CDO.

AAP