The invention discloses a dual-ring type seal oil automatic oil draining device and method of a hydrogen cooling electric generator. On the basis of the electric generator oil inlet accident principle, that is, in the running process of a dual-ring type seal oil system of the hydrogen cooling electric generator, before oil enters the electric generator, firstly, it can be reflected that the liquid level of a hydrogen side seal oil tank is high, then, an electric generator defoaming box is continuously filled with seal oil, and finally the oil enters the electric generator. Through draining of redundant oil and controlling the liquid level of the hydrogen side seal oil tank, oil entering of the electric generator can be avoided, and shortcomings in the prior art are overcome.