A dual-stage hybrid inflator and triggering a method thereof are provided. The dual-stage hybrid inflator includes a main casing, a central pipe, and a disc set, a first propellant chamber assembly, a second propellant chamber assembly, a pressurized gas, a first igniter assembly, a second igniter assembly and an exhaust hood. The main casing includes a bottom housing and an upper housing. The central pipe is fixed with the bottom housing and passed through the upper housing. A convective hole is disposed on the central pipe. The disc set, which is used to prevent the gas escaping from the main casing, is disposed on the top of the central pipe. The doublet propellant chamber, which is filled with different dosage of propellant, is initiated by the igniters disposed thereon in order to generate various degrees of gas depended on various degrees of collision.