A "low-bias-field method" for the formation of multi-branched domains (MBDs) in gaet bubble films has been introduced. By using this method, only a single MBD can be formed each time inside a pancake coil with an innerdiameter of 1 mm. The formation of MBDs is associated with the nucleation of vertical-Bloch-lines in their walls.Therefore, with the decrease of the bias field Hb from the "critical static bias field for multi-branched expansion"H[d], the pattes of MBDs become more and more complex, accompanying with the successive formation ofthree types of hard domains. The typical photos and the static properties of MBDs are presented.