The present invention presents a noise reducing device for the converter transformer and the method thereof. In the invention, the noise reducing device comprises the following components: a first sound insulating barrier (104) which is permanently connected to the top of the converter transformer (102) and is provided with a first edge (104a) and a second edge (104b); a second sound insulating barrier (106) which is permanently connected between the side surface of the converter transformer (102) and the cooler and is permanently connected to the first sound insulating barrier (104); a first sound insulating connecting plate (108) which is connected with the side surface which is on a first fire wall (12) and faces the converter transformer (102) and is detachably lapped with the first edge (104a); and a second sound insulating connecting plate (110) which is connected with the side surface which is on the second fire wall (12) and faces the converter transformer (102) and is detachably lapped with the second edge (104b). Through the invention, the installing and detaching can be conveniently executed when the excellent noise reducing effect is obtained.