Abstract: As a substance, electromagnetic wave has played and will continue to play an important role in the defense, economic and livelihood of the people. According to the table of the electromagnetic wave-spectrum, electromagnetic wave is described in detail. After making thoroughly research to the terahertz spectrum range of radio wave and light wave in electromagnetic wave, it's considered that the range is 0.15 THz to 6 THz in frequency or 2mm to 50μm in wavelength being scientific rationally. The results are important for the conduct of terahertz research and its applications .