The wavelength of terahertz wave is between those of infrared wave and microwave, with the characteristics of penetration, strong water absorption, and low photon energy, etc. Terahertz imaging has been are widely used in biomedical imaging, anti-terrorism security and non-destructive testing and other fields. The good penetration of terahertz wave is beneficial to detect the internal structure of objects. Phase-contrast imaging can better reflect the internal structure of objects, compared with simple terahertz intensity imaging. Continuous terahertz wave phase-contrast imaging can be divided into point-by-point scanning acquisition method with a single-point detector and full-field recording method with a surface array detector. The former has a low data acquisition rate and cannot image large samples quickly; the latter has a fast data acquisition rate, but also places higher demands on the detector's pixel size and dynamic range. Continuous terahertz wave digital holographic imaging records the hologram by a faceted detector, and then obtains the complex amplitude information of the sample by a reconstruction algorithm. According to different optical path structures, continuous terahertz wave digital holography can be divided into in-line digital holography and off-axis digital holography. In-line digital holography can make full use of the spatial bandwidth product of the detector, but requires a sufficiently high energy ratio of direct and diffracted light after passing through the sample, as well as the problem of twin image interference. Off-axis digital holography introduces a certain angle between the object light and the reference light, which solves the twin image problem and makes the reconstruction process simple.Off-axis image-plane digital holography uses a microscope objective to directly collect the imaging information of the object. Compared with off-axis Fresnel digital holography, this imaging method has fast computation and high resolution, and has been widely applied at visible wavelengths. Besides, this imaging method has been combined with some other high-resolution imaging techniques, resulting in multi-angle illumination digital holography, structured light illumination digital holography etc. However, due to the lack of terahertz devices and the strong absorption of terahertz by polar substances, the terahertz full-field phase-contrast imaging usually requires a compact and simple optical path structure. To the best of my knowledge, no relevant work on terahertz image-plane digital holography has been reported yet. In recent years, various terahertz devices such as lasers, detectors and gratings have been developed rapidly. New terahertz imaging elements such as large numerical aperture terahertz lenses and terahertz solid immersion objectives have emerged, providing strong hardware support for the development of terahertz imaging.In this paper, a continuous terahertz wave image-plane digital holographic imaging method based on TPX lens is proposed. The holographic recording and reproduction process is studied, and the quadratic phase distortion introduced by TPX lens is removed by surface fitting distortion correction. The digital holographic imaging system of terahertz image plane is built. The imaging resolution of the system is quantitatively analyzed by using an amplitude Siemens star sample. Then two phase samples of organic materials and biological samples are imaged. The experiment verifies the effectiveness of the phase contrast imaging method. The introduction of image plane imaging in terahertz band is conducive to improve the resolution and quality of terahertz imaging. It has a wide application prospect in biomedical imaging, nondestructive testing and other fields.