Shale is one of the main type of oil and gas reservoirs. The accurate characterization of trace organic matter is a hotspot and bottleneck in oil and gas exploration. Terahertz Time Domain Spectroscopy(THz-TDS) is employed to scan and analyze shale with different crude oil contents(ppm level). The results show that there is a monotonic relationship between THz parameter and the content of organic matter. With the increase of crude oil concentration, the attenuation coefficient of THz amplitude per unit thickness increases linearly. Combined with the theory of effective media, the linear relationship between THz dielectric constant and crude oil content below 200 ppm is determined. Therefore, THz-TDS can be used as an effective method for characterization of trace crude oil in shale, which is of great significance for the improvement of the exploration efficiency of oil and gas resources.