The problem brought by noise becomes an impediment to make GEHP commercialized. The paper establishes three-dimensional model of acoustic enclosure and model of double chamber fastness muffler on the bases of acoustics spectrum analysis coupled with acoustic theory. And the simulation of the noisy level of a GEHP with and without acoustical enclosure by the RAYNOISE software has been finished. Then the sound insulation device is designed according to the practical situation of the GEHP. And it can be concluded from experiment that the sound pressure level is sharply reduced to 77.8 dB (A) after fixed the sound insulation device, which improves the validity of the design about the noise control of GEHP.