We studied several aspects of the fracture of two dimensional dynamical lattices by the numerical simulation. The system consists of particles interacting by modified or truncated harmonic potential. We measured the crack propagation velocity on triangular and square lattices. A simple scaling rule for the crack propagation velocity is found for truncated harmonic potential. We also examined crack patterns and found that crack patterns under the isotropic tension is very similar to the snowflake pattern. The crack pattern under the inhomogeneous boundary condition is studied. The spatiotemporal oscillation recently studied by Yuse and Sano and by Taguchi is seen in the purely dissipative case. A simple phenomenological model of the spatiotemporal oscillation is presented.