Terahertz (THz)-wave in-line digital holography imaging is a new imaging technique based on interferometry record of terahertz wave. It exhibits advantages for the THz imaging because it only needs low coherence light source a simple optical structure, and has high resolution imaging and access to quantitative real-time complex complitude of light wave. We built a continuous-wave THz in-line digital holographic setup. By preprocessing hologram and phase recovery algorithm, we obtain amplitude and phase contrast images of the sample and effectively inhibit the conjugate image. Further, the feasibility of THz in-line digital holography is explored in biomedical detection.