Abstract: According to the experiments of 4 P.C. deep flexural members, the effects of shear span ratio and pre-stressed bars are taken into account in the calculation of shear capacity. The calculated cracking load and ultimate load are compared with those from test results. It is found that the shear span ratio had less influence on the shear capacity and the effective pre-stress is underestimated in code to calculate the shear capacity. Therefore, a modified equation is proposed considering the effect of pre-stress, which calculated shear capacity agrees well with the experimental results. It is also found cracking load is improved significantly after pre-stress is applied. Crack distribution shows that the truss-arch model can model the behavior of deep flexural members in shear.