A transmitted scanning terahertz imaging system,which has the <100>-InAs emitter of high power,wide frequency spectrum and the detector of high sensitivity and low noise,is presented.It owns the capacity of detecting something that has been shielded by some opaque dielectric materials.Moreover,spectroscopy data at each point of the sample can be acquired by using this system.Using these data the spectroscopy images can be rebuilt.Lots of THz images of sunflower seed sample by using various data processing methods based on the Fourier transform spectroscopy are given and compared.In addition,the several important factors of the sustem,including setup,measure to the beam,data processing described in detail,which are very essential to further research and application.