The exhaust device of steam turbine usually establishes vacuum rapidly using steam injection. The gas of the nozzle of the exhaust mixing device emits at high speed. The noise is very large. The muffler is designed to reduce the noise of the steam turbine’s exhaust devices. Referring to the principle of the separated expansion chamber muffler and connecting with practical production, we present a new type muffler. The design considers fully the peak frequency of the jetting noise of the nozzle and the noise attenuation of sound waves in the pipeline transmission etc. The muffler is small, light, anti- high- temperature and high-speed gases, and easy to be installed. The effect of noise reduction is obvious.