The Northern Territory Court of Criminal Appeal has increased the jail sentence of a man convicted of sexually assaulting a child.

In the Supreme Court last year, the man was sentenced to eight years in prison, with a non-parole period of five years, for raping a three-year-old girl at Tennant Creek in 2011.

The Director of Public Prosecutions appealed the sentence, saying it was manifestly inadequate.

The Court of Criminal Appeal heard the 23-year-old man had a history of abusing children.

Psychologists' reports found he had "an alarming lack of insight into his offending".

Justices Dean Mildren, Jenny Blockland and Judith Kelly this week allowed the appeal and increased the man's sentence to 11 years.

He will be eligible for parole in eight years.