Cao was born in 1918. Cao's father was Tuyển (Trung Thành) and his mother was Yến Nguyễn. His paternal grandparents were Thuận and Vẽn thị Nguyễn. He had a brother and a sister, named Vũ and Nhàn. He had two half-brothers and a half-sister, named Lai, Dương and An.