A new photometric method, which can reconstruct 3-D space coordinate (i.e.Z-distribution) of an object from one image under a point light source illumination, is proposed. The object is continuous convex with the perfectly diffused surface and the known uniform reflectance. To get the Z-distribution by solving the illuminating equation basing on the inverse square law for illuminance, an iterative algorithm has been developed. The tangent plane of the brightest surface element is firstly determined. The objective Z-distribution is finally obtained by iterating processes of calculating the Z-distribution treating the gradient distribution as constant. At each iteration step, the Z-distribution for the next step is determined from the present Z-distribution and the calculated Z-distribution which satisfies the illuminating equation, and the gradient distribution for the next step is calculated geometrically from the determined Z-distribution basing on the continuity of the surface. The usefulness of this method has been demonstrated by computer simulations.