The ACT Court of Appeal increased Alfred Chatfield's jail term after finding his conduct deserved a severe sentence and he appeared incapable of understanding that he must obey the law.

Chatfield, 44, grabbed the woman at knifepoint as she was walking home at 4.40am on September 20, 2009. He threatened to stab her and dragged her into bushes where he robbed and sexually assaulted her.

The woman's horrified partner, who had been speaking to her on the phone, heard her screams and phoned the police for help.

The woman eventually escaped after biting Chatfield on the hand and running on to Northbourne Avenue, where police found her shortly afterwards.

Chatfield was arrested several days later.

He had previous convictions for rape interstate and had been on a three-day drinking binge at the time of the offence. Chatfield was set for a trial but pleaded guilty in April last year to charges of sexual assault, indecency and aggravated robbery.

In June 2011, ACT Supreme Court Justice Hilary Penfold sentenced Chatfield to five years in jail with a non-parole period of four years. But the DPP took the case to the Court of Appeal, arguing the sentence was ''manifestly inadequate''.

It was argued that Justice Penfold handed down an inadequate sentence on one charge because she failed to take into account Chatfield's late plea of guilty, his lack of remorse and the fact that the maximum penalty was 12 years' jail.

The Crown also argued the judge had failed to properly accrue the sentences on the remaining three charges.

Chief Justice Terence Higgins and justices Richard Refshauge and Bruce Lander found the sentence was manifestly inadequate and Chatfield's conduct required a severe sentence. ''The respondent [Chatfield] made it clear in the coarsest terms that he intended to rape her by describing in graphic and vile terms that which he intended to do,'' they wrote.

''The respondent further terrorised the complainant by the acts of indecency which could have only reinforced in the complainant's mind the likelihood that she was to be raped.''

The judges also found Justice Penfold should not have applied different discounts to the sentences on the four charges but should have given the same discount for each sentence.

They said the objective circumstances of Chatfield's conduct called for a severe penalty while his subjective circumstances - his background and history - did little to suggest any reduction in the sentence.

The judges said women were ''entitled to walk the streets of Australian cities without being terrorised by offenders looking for sexual gratification''. They said Chatfield had spent nearly his whole life in the criminal justice system and ''appears unable to understand that he must obey the law''.

Chatfield's original sentence was set aside.

He was re-sentenced to a total of seven years and nine months' jail with a non-parole period of six years.