The judge told how the boy, now aged 18, began raping his sister when he was 13-years-old and she was just 9.
"Her innocence was taken away in the very place she should have found safe - her home"
Jailing the teen for ten years, Recorder Gareth Evans QC told him: "This was akin to a campaign of rape. This was an entrenched pattern of deviant behaviour.
"When you were 13 you began raping your own sister, who was then aged just nine years old.
"You continued raping her on a regular basis at least once a fortnight until she was 11. You caused her physical and mental anguish which must have been obvious.
"Her innocence was taken away in the very place she should have found safe - her home."
The judge added: "You callously used [your sister] for your own selfish needs. You made threats to her designed to stop her from telling people what was going on.
"That was sufficient to keep her quiet for a very long time. I have no doubt that you continued to rape your sister because you believed the threats had effectively silenced her."
The teenager has been ordered to serve 10 years in a young offenders' institution.