A transmission THz time domain spectrum system experimental device and the extraction method of related parameters are introduced. The spectrum characteristics in THz of green and yellow smoke screen materials are researched respectively to obtain the refractive index and shielding effect curves of the two materials. Experimental results show that the two materials have better shielding effect in visible and Infrared band, but has poor shielding effect in THz band. THz wave reconnaissance and detection has strong anti-jamming ability, which can make up the shortcomings of traditional visible and Infrared detection systems.