In order to study the loosening characteristics of jointed rock mass during blasting unloading in high stress area of underground powerhouse, the dynamic relaxation method and display calculation method are adopted to analyze the effects of different disturbance loads, lateral restraints and in-situ stress levels on the displacement of rock mass. The results indicate that: (1) Without lateral restraint, the loosening displacement of jointed rock mass in high stress field is mainly induced by blasting energy; with the increase of in-situ stress level in the direction of unloading, the loosening displacement produced by in-situ stress unloading is proportional to the elastic strain energy stored in the initial rock mass. (2) The displacement of rock mass under the coupling load is a nonlinear superposition of blasting impact and in-situ stress unloading, and with the increase of in-situ stress level, there is augmentation effect on the loosening displacement of rock mass under the coupling load. (3) With lateral restraints, the loosening displacement of rock mass in high stress field is significantly reduced due to the effect of friction and energy absorption of lateral rocks; with the increase of lateral stress level, the loosening displacement of jointed rock mass is mainly induced by the energy of the initial in-situ stress, i.e. the loosening displacement caused by in-situ stress unloading is larger than that caused by blasting impact.