This article is based on the holography experiment in university physics experiments. The setup has been improved by adding a microscope optical path and introducing a rotating glass slide in the reference optical path for continuous and quantitative phase modulation, thereby achieving the function of phase contrast microscopy. With the improved setup, phase contrast microscopic observation of onion epidermal cells was carried out. Compared with traditional microscopy, cytoplasm, nucleus and other microstructures that are difficult to observe without staining in traditional ways can be observed. The improved setup can clearly show students the application of holography in microscopy, producing positive teaching outcomes．