Abstract: The special curve affects the quality of parts of agricultural machinery, so it is important how to fair the special curves of parts of agricultural machinery. The criterion is minimum strain energy on fairing curves and surface. For many data points, the traditional energy method has too much storage space and computing speed is too slow. This paper presents a practical methodology of fairing for B spline curves based on the energy methodology. The method directly solves the equation by the B-spline properties. The improved method needs much less storage space and computing speed is much faster. The principle of fairing surface is: fairing the special curve of parts of agricultural machinery, then attaining the control point of the new suface. In this paper, plow surface is regarded as a sample. At last, the iso-curvature curve of parts of agriculture machinery surface before and after fairing was attained. The research result shows that the surface fairing was improved.