Background decrease method and adaptive filtering methods were proposed to solve the background removing problem in digital holographic microscopy in the in-line digital holographic microscopy.In-line digital holography microscopic system was set up, with which the digital holographic images of onion epidermis, the plant roots′ sample, the lamina stoma sample and the blood cell sample were reconstructed, respectively.In addition, the advantages of the proposed methods were demonstrated by calculating the light intensity distribution curves and the values of the contrast of images obtained with the in-line digital holographic microscope device.The results show that the backgrounds in the measured holographic interferometric fringes change with the experimental conditions and the sample itself.So that the backgrounds could be divided into three types, for each of which an appropriate method was proposed to achieve the best reconstruction image quality.The results may be helpful for reconstructing the better quality images.