It happened near Mono Street near G Street shortly before 8:00 am.
Officers said the female pedestrian died at the scene.
Police say the train traffic lights and railroad crossing signs were working at the time of the crash.
Traffic in the area was congested as the train remained stopped along the tracks, blocking Ventura and Mono Street. The road were expected to be closed for a couple of hours while officers continue their investigation.
Fresno Street was still open.