Abstract: Discretization is used to discretize line source to point source;and reflecting concave to a series of points on a volute curve so as to solve the surface area problem formed with a combination of the straight light and the reflected light on the measuring screen 25 meters away.Meanwhile the simulation based on Matlab is also achieved.The result of the simulation accords with the theoretical result.This example  deals with the application of the discretization thoughts in mathematical modeling and the advantage of Matlab implementation and its simulation.

Key words: mathematical modeling, discretization, simulation