A man who raped his young stepdaughter over a three-year period has been jailed for 16 years.

The girl's continuing difficulties were described by Christchurch District Court Judge Jane Farish at today's sentencing of the 39-year-old man, who has name suppression to protect the identities of his victims.

He was jailed for sexually violating his sister when she was 12 and he was 18, repeatedly raping his stepdaughter over a three-year period and doing indecent acts on her, repeatedly assaulting his stepson and assaulting his partner.

Defence counsel Lee-Lee Heah said the man was amenable to rehabilitation, and had expressed his shame and remorse. "I ask that the sentence not be so crushing that he loses hope and motivation to address his offending."

Crown prosecutor Dierdre Elsmore said it was evident that the man had caused marked harm to his stepdaughter, and her counsellor believed her symptoms were "only the tip of the iceberg".

Judge Farish said the man had sexually violated his sister as she slept in her bed.

He had begged her not to tell their mother and she had remained silent about it until the last year of her mother's life.

The sister had spoken out because she heard of the man abusing a second girl, the judge said.

"Her sole motivation was because she sees you as a serious risk of offending against other young females, and so do I unless you do something about it."

The judge said the man had taken every opportunity to sexually offend against his stepdaughter when she was aged from seven to 10.

"The effects on her are monumental," said the judge.

The girl was now alienated from her family.

She had only written contact with her mother and supervised contact with her siblings because there was overly sexualised behaviour between the siblings as a result of the man's offending.

The girl had post-traumatic stress disorder, sleep disorder and trust issues. She had only one friend.

"She is vulnerable to people taking advantage of her because she is not aware of boundaries in relation to her body space,'' the judge said.

''She has not reached puberty yet, and when she does, the enormity of your offending will overwhelm her." 

The judge said she had seen the man was distressed when his victims gave evidence at the trial where he was convicted.

"I accept you are sorry for the harm you have caused."

She declined to impose a non-parole term as part of the sentence so that he would be able to attend rehabilitation programmes sooner.

The man had received counselling but had not attended the STOP programme for sex offenders after a jail term for indecent assault on a girl in 1998.

- © Fairfax NZ News