Relatively high noise emitted from Transformers of in-door-substation in urban area has become the target of public complaints and the frequency is on the rise in these days due to an extension of transformer installations and new establishment of substations. The noise consist of harmonics of a specific frequency of the twice of the electricity frequency(60[Hz]), which is hard to control by using the general sound proofing techniques. In this work, several effective methods were discussed for reducing the noise from a transformer, which is transmitted through explosion preventing shutter and air tunnels. By applying to the actual site, the effects of the methods were verified.