A fiber-type terahertz (THz) time-domain spectrometer is designed by combining a fiber femtosecond laser with a fiber-coupled THz photoconductive antenna. The effect of laser polarization on the THz time-domain waveform, intensity, and spectral characteristics are studied experimentally. Via the precise control and the optimization of the polarization state of the femtosecond laser, the time-domain pulse splitting is eliminated, and a single-peak THz time-domain pulse with a high signal-to-noise ratio is obtained.