A quantitative layer by layer analysis method of 3D field is described. Electronic holography techniques are adopted in the method. It includes 1) digital recording of hologram, 2) numerical reconstruction of the complex amplitude at hologram plane, 3) calculating of the intensity at other plane parallel to hologram surface by diffraction formula in the spatial frequency domain. The whole 3D filed is reconstructed by the above three steps. Spatial resolution of this numerical reconstruction is given theoretically. An example shows the reconstruction of ideal 3D field formaed by computer simulation.