Abstract: Secondary fragments caused by explosion events are likely to induce serious casualty and disaster, so it is important to predict the probable properties of produced fragment for structural explosion design. In this paper, a numerical method for predicting fragments caused by damage of masonry wall impacted by blast pressure is proposed, which is derived by the application of continuum damage mechanics and micro-crack development mechanics in finite element method, and a homogenized material model is employed to represent the general masonry material properties. In order to refine the material model, strain rate effect of material strength is taken into account. The results demonstrated in this paper reflect that the homogenized masonry material model is reliable and more efficient to calculate the fragment size distribution. It is concluded that this numerical method can be used to predict the fragment size distribution of masonry wall in blast events.