The stabbing occurred just before 9:15 p.m., in the 5000 block of Newport Avenue, said San Diego police Officer David Stafford.
The woman ran away, but a witness followed her, Stafford said. At one point, the woman turned and threatened to kill the witness, he said.
Officers arrived and arrested the woman on suspicion of assault with a deadly weapon and making criminal threats, Stafford said.
The man who was stabbed was taken to a hospital.