The invention relates to a technology method for casting a flexible tie bar through circular ring type steel casting in a halving manner. The tie bar integrally having rigidity and provided with flexible section stress releasing holes is arranged on the steel casting cast through splitting of a half circle or a quarter circle or other circles. The reserved reversible deformations of the circular type casting in the splitting casting process are reduced to a great extent; the tie bar protects the casting in the solidification shrinkage process; and the defects such as cracking and shrinkage caused by the too large tie bar are overcome. The casting technology method with the technology tie bar as the main part and the technology reversible deformations as the auxiliary part in the process of preventing the casting from deforming for the large-sized steel casting is achieved, and therefore the subsequent repairing amount and the cutting amount during machining are reduced. Cost is reduced in practical production, and the production period is shortened.