Abstract: Using terahertz（THz）spectroscopy technique，oil time-domain spectroscopy of the waste oil（stand oil）and vegetable oil（soybean oil）in the range from 0 to 3.0 THz is measured.Refractive index ，absorption coefficient and other important optical parameters of the above oils are achieved by experiment，the results showed that the two oil properties in this band were significantly different，and changed as the frequency increases.Ripe soybean oil on high temperature and soybean oil could be identified by this method.It has important significance to detect the waste oil utilizing terahertz spectroscopy.