The terahertz time-domain spectrometer（THz--TDS）has a promising prospect in many fields such as spectroscopy, material characterization, security check and communication. Firstly, a stable fiber short pulse laser with a wavelength of 1560 nm and how to integrate the laser into the THz--TDS system are introduced.Then the THz--TDS system is used for nondestructive testing of several kinds of ceramic matrix composites(CMC).Especially the thickness accuracy of the thermal barrier coating reaches m level.Compared with the traditional methods, the terahertz wave provides a better solution because it has stronger penetration to CMC and can be applied flexibly.Finally, the high-resolution spectral analysis of low-pressure water vapor is accomplished based on the terahertz asynchronous optical sampling(THz--ASOPS).The spectral resolution reaches 10MHz, which is more than 100 times higher than the traditional THz--TDS.