In spite of the well developed theory and the practical use of the univariate B-spline, the theory of multivariate B-spline is very new and waits its practical use. We compare in this article the bivariate B-spline approximation with the polynomial approximation for the surface fitting. The graphical and numerical comparisons show that the bivariate B-spline approximation gives much better fitting than the polynomial one, especially for the surfaces which vary very rapidly.