The numerical approach to translatory coal bumps analysis is used to examine the effects of joint and coal seam stiffness on the outburst velocity, deformation magnitude of the opening wall and plastic zone length in the coal seam. A series of tests are performed by varying the joint dip angles, spacing normal to joint tracks, joint block size and coal seam stiffness ratio to the surrounding rock. Results of joint and coal seam stiffness effects analysis indicate that joint dip angle, interval spacing, block size and coal seam stiffness ratio have profound influences on coal bumps. The increasing of interval spacing and joint block size can generate larger roadway deformation, lower roadway deformation velocity and longer plastic region in the coal seam. Higher stiffness ratio can also result in larger deformation, higher deformation velocity of opening wall. Coal bumps conditions deteriorate as the dip angle rotated to 90 degree or the elastic zones disappear in the whole active zone of coal seam for different spacing distributions.