Timothy Leonard Gordon Farmer, of Albany, was sentenced in the WA Supreme Court after pleading guilty to the manslaughter of Mason James Coughlan on October 30, 2006.
Justice Eric Heenan said Farmer had beaten Mason over a two-week period using tree branches, garden hoses and thongs inflicting injuries so severe they had filled seven pages of a pathologist's report.
It was one of the worst cases of child cruelty to come before the courts, Justice Heenan said.
"The events which led to Mason's death present an agonising picture of violence, cruelty and insensitivity towards a young, helpless, terrified child," he said.
"The post mortem … makes extraordinarily grim reading, even for those acquainted with incidences of death and violence.
"There was almost no part of the child's body which did not show extreme bruising and multiple abrasions.
" .. More extensive post mortems investigation of the internal organs and tissues showed even more serious effects."
Justice Heenan said Mason had been three years and six months old when Farmer began a relationship with his mother.
He soon began beating him, "ostensibly for correction or discipline".
On the night the child died, Farmer had used a section of hose to beat the screaming boy after he had wet his pants.
While he was in the bathroom with Mason, the boy's mother said she had heard noises coming from the bathroom as though Mason's head was hitting the wall or the shower screen.
When Farmer carried the child into Albany Hospital about 10.30pm on October 30, 2006, he had already stopped breathing.
Resuscitation was attempted but he was "cold and lifeless", Justice Heenan said.
Asked by nurses why the boy had so many bruises and abrasions, Farmer told them he had "pissed the bed and got a smack and was put in the shower".
Sentencing Farmer, Justice Heenan said: "It is almost beyond belief that such a young child had been subjected to such trauma".
He said Farmer's 10-year sentence was the maximum available after truth in sentencing provisions and his guilty plea were taken into account.
He added Farmer had come from a family of nine whose alcoholic father died at 40 in "distressing and abject circumstances".
Farmer himself had first overdosed on drugs at 11 and had numerous convictions dating back to 1985.
But outside the court, the child's family said the sentence was too lenient.
"What can we do? We can't even comment in there. I don't think it's fair," one woman said.
Another said: "You get somebody who torments a little kid, puts him in salt water, gives him bruises from head to toe, he has his skull cracked, and gets 10 years."
Farmer's mother said the sentence was too severe.
"It's too much as far as I'm concerned because I'm his mother," she said.
"But I know it's his punishment and I understand. But I can see the light at the end of the tunnel because he'll come out of prison."
Farmer was sentenced to another year, to be served cumulatively, on a charge of assault in a separate matter.