Abstract: Because of no definition given to the smeared crack model in crack influencing zone, a calculation method based on the principle of equivalence of strain energy is proposed to determine the crack element length, thus enabling the conventional rough modeling process to be more practical and finding out the dependence of crack depth on crack influencing zone. It is found that the crack influencing zone becomes maximum when the dimensionless crack depth is 0.4 which is 0.443 times as large as the beam height. A numerical example is given and shows that the simulation results by use of the improved model is basically in conformity to testing results.