Three dimensional (3D) body scanning has been of great interest to many fields, yet it is still a challenge to generate accurate human body models in a convenient manner. In this paper, we present an accurate 3D body scanning system based on structured light technology. A four-step phase shifting combined with Gray-code method is applied to match pixels in camera and projector planes. The calculation of 3D point coordinates are also derived. The main contribution of this paper is twofold. First, an improved registration algorithm is proposed to align point clouds reconstructed from different views. Second, we propose a graph optimization algorithm to further minimize registration errors. Experimental results demonstrate that our system can produce accurate 3D body models conveniently.