Numerical reconstruction is the focus problem of the digital holography. However,the techniques that have been discussed can only obtain the 2-D light field distribution. In this article,a method about 3-D rebuilding based on numerical reconstruction of the hologram is proposed,by which the genuine 3-D image can be numerically reconstructed. A number of 2-D light field intensity distributions of the digital hologram are numerically reconstructed on the different depth planes. Then,the focus measure evaluation of the gray level variance is applied. By finding the maximum focus measure,decide on the depth information of each image point. The experiment confirms that the method can materialize the 3-D rebuilding of the,reconstruction image,that is,3-D profile information of the object can be obtained by the proposed approach. So digital holography can be a very promising technology for non-destruction 3-D shape measure. In addition,3-D reconstruction can provide an effective way to the image evaluation of the hologram and validating the correctness of the CGH algorithm.