The invention provides a sound insulation device for treating noise. The sound insulation device comprises a foundation pier and an arc-shaped sound insulation plate arranged on the foundation pier. A groove is formed in the upper end face of the sound insulation plate. An extending section matched with the sound insulation plate in shape is slidably arranged in the groove and comprises an iron plate and a rock wool layer which are connected in sequence. A dovetail groove is formed in the wall of the groove at the upper end of the sound insulation plate. A dovetail bulge is slidably arranged in the dovetail groove. A magnet capable of being in magnetic connection with the iron plate is arranged on one side of the upper end face of the dovetail bulge. The sound insulation plate can insulate the noise produced by a highway so as to avoid damage to the health of a human body. The extending section is slidably arranged in the sound insulation plate, so that the height of sound insulation can be adjusted according to the position of a noise source, and it is guaranteed that the noise produced by the highway can be fully blocked and absorbed.