Abstract: The distribution and change of fluid pressure have significant influence on the deformation and stress state of surrounding rockmass of the boreholes and caverns，which is related to many engineering phenomena. However，this is a dynamic coupling process involving several variables and responses, and has not been solved by analytical method yet. Also，study of the dynamic variation of fluid pressure can hardly he approached by physical mode1． In this article，we will，taking the discharging gas through borehole as an example，analyze the mechanism of some related engineering phenomena and appropriate countermeasures by applying numerical simulation and using the outcomes of experiments which were carried out on both macro and micro scales. There are two basic findings：1)During the process of gas discharge，pressure gradient of gas near the borehole wall decreased greatly，the Mohr’s stress cirde enlarged ，the stress state deteriorated and the plastic range expanded ．2)Outside the above area，both the maximum principle stress and the minimum principle stress increased，so did the effective stress and the influence range of stress redistribution. Based on the two findings described above，the following mechanisms for the deformation of surrounding rockmass in the process of gas discharge are proposed：in the area where the pressure gradient of gas decreased greatly，shear-and-tensile failure occurred．Just outside this area，the stress increased and its influence range enlarged, the deformation of surrounding rockmass accumulated accordingly. Furthermore，decrease of gas pressure against the grain surface could lead to the development of internal off-load crevice．These mechanisms has been illustrated by many related engineering phenomena．When gas pressure decreased， the conductivity coefficient of coal increased accordingly，and deformation of surrounding rockmass accumulated．Finally，we believe that gas discharge can release not only gas expansion energy，but also deformation energy of surrounding rockmass．Consequently, it is obviously helpful to reduce the possibility of outburst．