In order to distinguish real image from conjugate image and zero-order term in digital hologram, a new method of image reconstruction is proposed. This method using the theory of coherent diffraction imaging (CDI) reconstructs accurate image without zero-order diffraction and conjugate image. The method proposed includes two processes: the first is to measure the object intensity distribution, the hologram and the reference light intensity distribution; the second is the reconstruction of object by using computer. The convergence speed and image quality are improved because of the coherent light. Basic principle and simulation result are described. And the experiment of image reconstruction of biological sample plates is carried out.