Measurement of basis weight which is one of the most important physical indexes of paper sheet is of decisive importance in paper making process. However, this problem has not been well solved so far. Terahertz time domain spectroscopy is a newly developed spectroscopy technique based on femtosecond laser technology, and has been studied in some other research fields. The purpose of this work is to study the feasibility of applying terahertz time-domain spectroscopy technique to the measurement of paper sheet basis weight. Two principles were presented in this study. One was based on terahertz amplitude attenuation and the other was on terahertz delay time. Experiments were carried out to verify the theoretical analysis and compare the performances of these two proposed principles. The experimental results show that delay-time-based method is better than amplitude-attenuation-based method in terms of linearity and accuracy. The research work indicates that the method based on terahertz delay time is feasible for paper basis weight measurement. And it may provide a new solution for paper basis weight measurement