A District Court judge has jailed a former WA police officer for sexually abusing a child more than 40 years ago, telling the man he left his victim with a lifelong sentence.

The 67-year-old pleaded guilty to two counts of indecent dealing with a child under 14, on an unknown date between 1979 and 1984.

The man, who the ABC has not named to protect his victim's identity, insisted the offences took place before he joined the police force in 1981.

Appearing in the Bunbury District Court on Monday, he was jailed for 14 months, and will be eligible for parole. 

Victim wore hidden wire

The court heard he sexually abused the child, who was aged between four and nine years old, while playing tickling games in a bedroom.

But it took decades for the abuse to come to light.

Prosecutor Alan Dungey said the victim's mother confronted the man in 2020.

The victim, who is now in her late 40s, wore a covert recording device to meet with the man in Busselton in 2021, to discuss the events which took place four decades ago.

He admitted to the abuse, and detectives arrested him on June 15, 2021.

He pleaded guilty in February.

Lasting damage

The man's lawyer, Michael Devlin, said his client had insight and remorse into his behaviour, and had sought counselling for what he had done while aged in his mid-20s.

Mr Devlin said his client had been emotionally immature, and since then had lived a "blameless life".

He said he had served more than 30 years in the WA police force in various roles, before leaving in 2017. 

But Mr Dungey said while the man had been able to go on to enjoy a long and successful career, his victim still suffered as a result of the abuse. 

Judge David MacLean said only immediate jail was appropriate.

He referred to the victim impact statement, in which the victim said she suffered from constant shame and guilt. 

"She is still attempting to come to terms with her psychological and emotional demons," he said.