Cao's carelessness was "at the highest end", Judge Phillips said.
"You continued to drive after you knew you were tired and drove completely on the wrong side of the road," Judge Phillips told Cao through an interpreter.
Cao stood silently with his head bowed throughout his court appearance.
Police prosecutor Tim Hambleton said Cao told police he turned into the right-hand lane - as was the practice in China - when entering State Highway 1 from Moeraki.
Cao knew he should have been driving on the left-hand side, but was tired and made a "terrible mistake", Mr Hambleton said.
Cao arrived in New Zealand on February 17 to holiday with his family.
He hired a Ford Ranger in Auckland to tour New Zealand.
Cao spent the night of February 20 in Christchurch and left about 10am to travel to Queenstown.
The family stopped at Moeraki Boulders to take photographs before continuing their travel about 4.50pm, Mr Hambleton said.
About 1km after turning on to State Highway 1, Cao crossed the centre line.
As he approached the brow of a hill on the highway, he saw the Marris family's vehicle.
The drivers of both vehicles attempted to avoid each other, but veered in the same direction and collided head on.
There was little traffic on the road at the time, the weather was fine and the road was dry, Mr Hambleton said.
The section of road was marked with yellow no-passing lines.
Ruby died at the scene and her parents, Tristan and Kimberley, suffered serious injuries.
The Marris' two other children, Georgia, 9, and Sophie, 7, suffered moderate injuries.
The family's surviving members were taken to Dunedin Hospital.
Cao's 60-year-old mother, who was a passenger in the rented four-wheel-drive, was also seriously injured and was taken to Oamaru Hospital.
Cao was convicted and remanded on bail for sentencing on June 9.
Dangerous driving causing death is punishable by up to 10 years' imprisonment.