Effect of grain boundaries (GBs) on elastic shock wave in graphene is investigated by molecular dynamics simulations. Bicrystal graphenes with symmetrical GB are shocked along directions perpendicular and parallel to GB. For perpendicular shock loadings, double elastic shock waves emerge in form of quasilongitudinal (QL) and quasitransverse (QT) waves, since the loading direction is neither zigzag nor armchair. GB attenuates the QL wave and gives rise to new QT waves propagating into grains. Transverse particle motion in the elastic shocks can induce small lattice rotations and different oriented regions, whose number increases upon the passage of waves through GB. Upon shock loadings along GB, transverse particle motions of opposite direction generate in the two grains, and change the pressure distribution right behind wavefront, and then result in deviation of shock wave from planar loading or “V” shaped wavefront turning at GB. The above phenomena are attributed to the turn of grain orientation at GB and transverse particle motions induced by lattice symmetry reduction upon shock compression.