The invention provides a ventilation and noise reduction device of an indoor transformer. The device comprises a ventilation louver and an axial flow fan located in wall body openings, a first-type active control mechanism located outside the louver, and a second-type active control mechanism located outside the axial flow fan, wherein the ventilation louver and the axial flow fan are used to implement ventilation and heat dissipation and ensure safe and stable running of the indoor transformer, and the louver and the axial flow fan are located on two wall bodies respectively; the first-type active control mechanism is used to reduce noise radiated by the indoor transformer from the ventilation louver to external environments; the second-type active control mechanism is used to reduce noise radiated by the indoor transformer from a ventilation opening of the axial flow fan to the external environments and reduce noise radiated by the axial flow fan to the external environments; and the first-type active control mechanism and the second-type active control mechanism compose the active noise reduction system.