The 26-year-old man, who cannot be named for legal reasons, repeatedly punched the girl with a closed fist and wrapped his hands around her neck on the evening of April 1 this year at an address south of Wollongong.

Court documents said the girl's mother left her four children - three of whom are the man's biological children - at home with him while she went across the road to get a cigarette just before 8pm.

While she was gone, the man began yelling at his step-daughter to clean her room and go to bed.

"The accused punched [the child] in the left side of her head with a closed fist," court documents said.

"He grabbed [her] around the neck with both hands, applying pressure, and then punched her in the right knee, causing pain."

The girl's mother came home five minutes later, at which time her partner turned on her, accusing her of spending too much time away and calling her names.

He locked her outside for a short time before opening the door and running towards her, causing her to turn and flee up the driveway.

She ran to a neighbouring house and contacted police.

Officers arrived a short time later to discover the man down the street on the side of the road.

He was arrested and charged with two counts of common assault, one count of intentionally choking a person and one count of contravening an apprehended domestic violence order.

The man had been due to contest the charges in court on Monday but entered pleas of guilty before the hearing began.

The case was adjourned to October 21 for sentencing.