Abstract: The influence of nonlinear shock on the focusing property of femtosecond pulsed beams was studied through numerical simulation by using the modified(3+1)-dimensional nonlinear Schrodinger equation,taking into account of diffraction effects,space-time coupling,normal dispersion,and cubic nonlinearity.The self-focusing properties of the 90fs pulsed beam were analyzed and discussed in the absence and in presence of shock effect respectively.The results show:The space-time coupling,dispersion,and Kerr effect together will cause the pulse filament,amplitude descending and its width broadening.As implied by the functional form,space-time coupling relates to the dispersion will produce a time shift.The shift increases with distance and dispersion,and that the self-steepening effect will result in the peak power decreasing greatly,moreover it will weak the pulse self-focusing effect.