Complex surfaces have been widely used in engineering. However, the current general-purpose CAD systems do not provide the modeling method of some kinds of complex surfaces such as parametric surfaces. In this paper, complex surfaces are generated by calculating the coordinates of the data points on the surfaces, creating the data files, importing the files into UG (Unigraphics), and then making use of the surface modeling functions of this software. Taking a bicubic B-spline surface for an example, the main steps of modeling of complex surfaces are presented and the modeling errors are analyzed in detail. A test is conducted to verify this approach.