Oscar Pistorius -- I'M GETTIN' OUT!!!

Oscar Pistorius will be released from prison on Tuesday -- and moved to house arrest -- just one year after he was convicted of shooting and killing his girlfriend Reeva Steenkamp.

A lawyer for Steenkamp's family confirmed the news ... but it's clear, they're pissed.

"Nothing will bring Reeva back," the Steenkamp attorney said ... "[Her parents] are not surprised at all by this announcement. They expected this."

The South African olympian -- aka Blade Runner -- was convicted of culpable homicide for shooting Steenkamp in his home in South Africa on Valentine's Day in 2013. Pistorius claimed he mistook her for an intruder.

Oscar was sentenced to 5 years behind bars -- but a South African parole board has greenlit the move to allow him to go to house arrest ... reportedly a common procedure out there.