Four kinds of organic solvents, including positive hexane, liquid paraffin, ethyl alcohol, and water, were measured by using terahertz time-domain reflection spectroscopy. According the experiment models, two methods can be used to extract optical parameters. Refractive index and absorption coefficient for these four solvents were extracted with two methods and were compared with the results obtained by transmission measurements, which verified that these methods are correct. This work solved the problem that the optical parameters of sample absorbing strongly terahertz cannot be measured and extracted by using terahertz time-domain transmission system.