The ultrafast nonlinear optical properties in liquid CS2 are investigated by the femtosecond optical Kerr shutter technique at wavelength of 800 nm.Measurements for the dependence of Kerr signals on the polarization angle between the pump and probe beams show that the Kerr signals induced by 30 fs pulse laser arise mainly from the photoinduced birefringence effect ,but not from a laser-induced transient grating as absorbed when using a 200 fs pulse laser.The OKE signal intensity increases with the increases of the intensity of pump beam.