The dynamic elastic-plastic field near a crack tip running in a strain-damage material is investigated. The medium is assumed to obey the J 2 flow theory and the damage rule is given asymptotically in a form like power-law strain softening. For the plane strain problem the constitutive relation is derived and much simplified for the case of Poisson's ratio v = 1 2 . The asymptotic equations of the dynamic elastic-plastic field are given and solved for mode I crack. The displacements, strains and stresses are expanded in series of ln R r ; therefore the asymptotic behaviour of the field is revealed. The results show that at the crack tip the strain possesses the logarithmic singularity (ln R r ) δ while the stress is like (ln R r ) −nδ .