Abstract: A new method for fast image generation of quadratic surfaces based on equi-intensity curves is proposed on the basis of the geometric model and the shading model analysis. Equations of the equi-intensity curves are derived under the usual model of diffusive reflection and Phong's model of specular-surface reflection. Two key problems are solved theoretically:1. how to compute the projective equations of the equi-intensity curves'.an approximation which yields good compromise between precision and efficiency is presented;2. how to calculate the coordinates of points on the equi-intensity curves. In addition, analysis for efficiency and precision of the algorithm is given.