A woman accused of murdering her ex-lover after drugging him and mutilating his genitals has been formally denied bail in a Sydney court.

Jian Chen, 48, is charged with one count of causing grievous bodily harm with intent to murder and one count of murder.

She is accused of using sleeping pills to spike the soup she gave her former partner at her North Ryde home on February 9.

Xian Peng, 48, had only recently returned to Australia from China with a new girlfriend, according to police.

Once Mr Peng was asleep, Chen allegedly bound his hands and feet and stabbed him a number of times in the neck and groin, before cutting his penis and scrotum.