With the maturation of terahertz (THz) technology, the THz digital holography, which is one of the most important development directions, gradually exhibits the application powers in various research and industrial fields. The work in the improvement and applications of the THz digital holography in recent years is discussed. A THz holographic imaging system with a high spatial resolution, high signal to noise ratio, and polarization information measurement ability is built. Furthermore, it is demonstrated that this imaging system can be used to check the performances of THz planar elements, measure transmission modes of the THz waveguide, and observe the Gouy phase shift of the converging THz beam. This work is valuable for promoting the practicability of the THz digital holography.