A rotor assembly comprising: a compressor section comprising a plurality of compressor rotor discs; a turbine section comprising a plurality of turbine rotor discs; a tie rod that passes through the compressor section and the turbine section and extends; a fastening portion coupled to both ends of the tie rod and configured to fasten the compressor section and the turbine section to the tie rod; a torque tube disposed between the compressor section and the turbine section so as to forcibly connect the compressor section and the turbine section; and a sealing portion installed in a space between facing surfaces of the plurality of compressor rotor discs to be coupled to one another and in a space between facing surfaces of the plurality of turbine rotor discs, and configured to seal the space between the facing surfaces of the plurality of compressor rotor discs to be coupled to one another and the space between the facing surfaces of the plurality of turbine rotor discs, characterized in that slots (201a, 211a) are formed in the facing surfaces of the plurality of compressor rotor discs and the facing surfaces of the plurality of turbine rotor discs, and the sealing portion comprises a sealing plate (110, 110a) formed of a first material and inserted into the slots (201a, 211a) and an auxiliary plate formed of a second material and coupled to one side of the sealing plate (110, 110a), the second material being softer than the first material, wherein the slots (201a, 211a) are formed in each of the compressor rotor discs and the turbine rotor discs to have ring shapes in a circumferential direction, the sealing plate (110, 110a) and the auxiliary plate having a ring structure, and the auxiliary plate attached to and coupled to an inner circumferential surface of the sealing plate (110, 110a). a compressor section comprising a plurality of compressor rotor discs; a turbine section comprising a plurality of turbine rotor discs; a tie rod that passes through the compressor section and the turbine section and extends; a fastening portion coupled to both ends of the tie rod and configured to fasten the compressor section and the turbine section to the tie rod; a torque tube disposed between the compressor section and the turbine section so as to forcibly connect the compressor section and the turbine section; and a sealing portion installed in a space between facing surfaces of the plurality of compressor rotor discs to be coupled to one another and in a space between facing surfaces of the plurality of turbine rotor discs, and configured to seal the space between the facing surfaces of the plurality of compressor rotor discs to be coupled to one another and the space between the facing surfaces of the plurality of turbine rotor discs, characterized in that slots (201a, 211a) are formed in the facing surfaces of the plurality of compressor rotor discs and the facing surfaces of the plurality of turbine rotor discs, and the sealing portion comprises a sealing plate (110, 110a) formed of a first material and inserted into the slots (201a, 211a) and an auxiliary plate formed of a second material and coupled to one side of the sealing plate (110, 110a), the second material being softer than the first material, wherein the slots (201a, 211a) are formed in each of the compressor rotor discs and the turbine rotor discs to have ring shapes in a circumferential direction, the sealing plate (110, 110a) and the auxiliary plate having a ring structure, and the auxiliary plate attached to and coupled to an inner circumferential surface of the sealing plate (110, 110a).