The embodiment of the invention discloses a de-noising apparatus of a converter transformer. A main body of the transformer is placed in a 'BOX' by means of a new technology for treating the noise of a large-sized converter transformer by using a firewall and a valve wall at two sides of the converter transformer to carry out closed acoustic treatment to the main body of the transformer. In order to provide convenience for examining and repairing equipment, a self supporting sound insulation and absorption compound structure is adopted in both a 'BOX-IN' front board and a 'BOX-IN' top board in the embodiment of the invention. As partial sound insulation and absorption boards and steel frames can not be disassembled, all nodes are connected by bolts, thus being assembled and disassembled rapidly. All parts are manufactured by molding, do not require cutting on site and have high processing and reusing rate.