A man has avoided prison after assaulting his former de facto partner with a rock, bruising her eye and causing cuts to her arms.

Jason Phillip Pennington, 32, was given an eight-month jail sentence, suspended for 12 months.

If Pennington reoffends during that time, the sentence will be activated.

The court heard on December 18 Pennington and his partner, with whom he has a one-year old child, were drinking in Boulder.

The pair were walking along a street when they decided to sit down for a rest, and began to argue.

During the argument, while still on the ground, Pennington picked up a rock and struck the victim above her left eye.