The digital holography technology is based on holography. A photodetector device is used instead of a holographic dry plate as a recording medium. The light intensity and phase information of the object is recorded, and the reproduced image is obtained by using a computer to realize the holographic reproduction process. Digital holography can perform noncontact, high-quality measurements and can obtain three-dimensional position information. This paper presents an off-axis digital holographic underwater microbiological detection method based on Jamin interferometer. For the identification of underwater microorganisms, the Euclidean distance identification method based on Hu invariant moments was used to identify underwater microorganisms. The experimental results show that the off-axis digital holography system constructed in this paper can clearly capture the underwater microorganisms, and effectively identify the paramecium and the feasibility of the verification system and algorithm.