In the paper,the weighting function is investigated which plays an importantpart in nonlocal strain softening damage model.Its expression is derived and behaviours including therelationship between the weighting function and the characteristic length of heterogeneous materialsare analyzed.The method for calculating monlocal quantities is also presented.Selecting of theweighting function has important significance for more objectively establishing nonlocal damagemodel and analysis of damage of heterogeneous materials by numerical methods.