A 39-year-old man who repeatedly raped his stepdaughter over three years and sexually violated his young sister has been jailed for 16 years.

The man's sentence, handed down at the Christchurch District Court on Thursday, was also for doing an indecent act on his stepdaughter and assaulting his stepson and partner.

The man's name is suppressed to protect the identities of his victims.

The court heard how the girl was left with post-traumatic stress disorder, a sleeping disorder and trust issues after being raped by her stepfather from the age of seven, the Christchurch Court News reported.

The man also sexually violated his 12-year-old sister when he was 18.

His lawyer, Lee-Lee Heah, told Judge Jane Farish that the man was remorseful and ashamed of what he had done.

Judge Farish said the man was at risk of reoffending if he did not get treatment.

The offending has had a "monumental" impact on the girl's life and would only get worse as she got older, she said.