Abstract: The determination of deformation modulus of jointed rock mass is of great importance for the design and stability analysis of deep rock mass engineering. Therefore, it is of great engineering significance to study the effect of confining pressure on deformation characteristics and failure modes of jointed rock masses. Based on discrete element numerical simulations and laboratory testing data, triaxial numerical simulations on deformation and failure of blocky jointed rock masses with two pre-existing joints under different confining pressures were carried out. The main conclusions are as follows: (1) The deformation modulus of blocky jointed rock masses increases with the increase of confining pressure. When the confining pressure is more than 4 MPa, the change of deformation modulus tends to be gentle; (2) The failure modes of blocky jointed rock mass can be divided into two types: the sliding failure along the existing joints and the shear failure across the whole rock mass. With the increase of confining pressure, the failure mode of the blocky jointed rock mass model develops from sliding failure with joints to shear failure in intact rock; (3) For 1+2, 2+3, 3+5 and 5+7 blocky jointed rock mass models, the confining pressures at which the failure mode changes are 0.5, 1.0, 4.0 and 4.0 MPa, respectively.