A foster father in Cairns has been jailed for sexually abusing a six-year-old girl who was in his care.

The 41-year-old man, who is not named to protect the child, was found guilty of 12 offences at Cairns District Court on Thursday.

The abuse came to light after police raided the mans home last September, uncovering a cache of child pornography, including a 55-second video and pictures he took of the six-year-old girl while he sexually abused her.

Details of the horrific acts he performed on the girl were discussed in court as Judge Judge Brian Harrison declared it as 'one of the most serious examples of a breach of trust that I have ever seen'.

A 41-year-old man was found guilty of sexual abuse offences at Cairns District Court on Thursday

'You so callously and so cruelly abused that trust that was placed in you by authorities and took advantage of her for your own sexual gratification,' Judge Harrison said, according to the Cairns Post.

The man and his then-fiance were registered foster carers when they began caring for the girl and her two sisters in early 2016, the court heard.

Crown prosecutor Rebecca Christiansen said the man later admitted to police he had been sexually attracted to young girls since he was a teenager.

The man and his then-fiance were registered foster carers when they began caring for the girl and her two sisters in early 2016 (stock image)

Police also found more than 6700 pornographic images, many of which featured children, in the home in Cairns' southern suburbs.

One image also contained acts of bestiality.

Police located the man after he had shared some of the material online.

Ms Christiansen said the former foster father tired to shift the blame for his actions onto the child during a police interview, and showed a 'lack of remorse'.

'This was a high level gross abuse of trust. It will have a significant long and short-term affect on the child,' she said.

He was sentenced to six-and-a-half years in jail but will be eligible for parole in November next year.