The invention provides a premixing chamber of an aircraft engine flame tube and a design method thereof. The premixing chamber is of a cylindrical structure, and the premixing chamber is arranged between a fuel nozzle, a flame tube cyclone outlet and a flame tube head, to achieve oil and gas premixing. The method for designing the premixing chamber of the aircraft engine flame tube comprises the following steps: (1) determining the inner diameter D of the premixing chamber; and (2) determining the axial length L of the premixing chamber; (3) determine the distance P of a main spray cone angleof the fuel nozzle at a droppoint of the wall surface of the premixing chamber; (4) determining that an auxiliary spray cone angle of the fuel nozzle does not collide with the wall surface of the premixing chamber, and flame is directly sprayed into the flame tube. According to the premixing chamber of the aircraft engine flame tube and the design method thereof, the size of the premixing chambercan be accurately designed, the workload in the combustion chamber testing process is reduced, manpower and material resources are saved to the largest extent, and the premixing chamber has an obviouseffect of reducing exhaust smoking of a combustion chamber and improving combustion stability of the combustion chamber.