Emergency services were called to the scene, off Forge Lane, following a report of a body seen line-side shortly before 4pm on Sunday.
Residents reported seeing a heavy presence of police and ambulances at the scene.
Officers, along with paramedics, found the pensioner near to the lines and transported the 75-year-old to hospital.
A spokeswoman for British Transport Police said: "Officers were called to the lines close to Cradley Heath at 3.41pm on Sunday after reports of a casualty on the tracks.
"Paramedics also attended and a 75-year-old man was taken to hospital where he remains in a critical condition."
"His family have been informed and the incident is not being treated as suspicious."