Based on multi-source data, a fitting geological surface is required to achieve the balance among accuracy specification, continuity and storage. An approach of complex geological surface reconstruction which combines interpolation with approximation based on NURBS(non-uniform rational B-splines) technique is presented. The algorithm adopts the skinning method for densely and uniformly distributed data in the key region, and it ensures that all original data are on the built surface strictly. For the discrete data in the peripheral region, NURBS approximation fitting method is used to construct the corresponding surface, which approximates the data fully under the required accuracy. Finally, the integrated surface is analyzed and modified by checking the rationality of geological structure, geometry and accuracy. The instance shows that the approach can satisfy practical demands of engineering geologists and offer elements to further 3D geological modeling.