An integral expression for the time domain output response of traveling wave (TW) electrooptic phase modulator is derived by using the scalar wave equation and Fourier transform technique. In the case of a Gaussian modulating pulse, the temporal dependence of the output modulated phase amplitude was calcauated. The plots showing the effect of velocity mismatch and microwave attenuation on pulse shape, amplitude, and width was given. The method proposed is generally applicable to the time domain analysis of TW modulators.