A Canberra man who downloaded child pornography by accident has been handed a suspended jail sentence.

Clinton James Morosi, 36, pleaded guilty in the ACT Supreme Court to charges of accessing and possessing child porn.

In 2011, police found 1002 illegal videos and images on three computers and an external hard drive owned by Morosi.

The court heard much of the material depicted girls aged 16 to 18, but a small number of items featured children younger.

The defence team claimed their client accidentally downloaded the illegal material from the internet among packs of legal, adult content.

A presentence report found Morosi was at low-risk of reoffending.

Justice John Burns said the 1002 videos and images were collected over four years, were never shared or traded, and constituted a small percentage of his about 400,000 file pornography collection.

The judge accepted, at the time of downloading the material, Morosi had been seeking self-posted style content featuring girls aged 16 to 18.

The judge also accepted the offender believed material showcasing girls in that age range were legal.

But Justice Burns said Morosi had been naïve to believe there had been no exploitation because the material appeared to be self-posted.

The judge sentenced the offender to three years jail, to be fully suspended upon entering a three year good behaviour order and the payment of a $500 security.