A numerical method for producing and reconstructing Fresnel off line computer generated hologram(CGH) of a 3 D object is described in this paper.Based on the Born approximation,an ideal 3 D object model is builded.A CGH of the 3 D object is generated through the method of Burch coding.Using convolution and fast Fourier transform(FFT) algorithm to calculate diffraction integral,the CGH is reconstructed by digital focus method.The variety of layers of the 3 D object is reconstructed through using different distances between reconstructed image and CGH.By using digital filter method,twin images and zero order diffraction images are eliminated and clear real images are obtained.The 3 D objects CGH is presented in this paper,together with the results of numerical reconstruction of different sections.