A Brooklyn man strangled his girlfriend yesterday while their 7-year-old daughter was home, police said.

Cynthia Lopez, 29, was arguing with Daniel Elias, 28, shortly before 6 a.m. in their apartment on 50th Street in Sunset Park when he allegedly attacked her.

Their daughter, Destiny, was in another room and did not witness the slaying, police sources said.

Elias later claimed that Lopez charged at him with a knife, officials said. He was charged with murder.

A relative of Elias said there may have been a fight over the boyfriend’s accusations that Lopez was cheating on him.

The relative said the pair had a stormy, off-and-on relationship.