Abstract: It is one of the main functions of fabric CAD system to simulate the fabric according to its yarn structure,weaves and patterns.To acquire more effective and realistic simulation,this thesis transforms the rendered drawing from 2-D to 3-D, and introduces trace depth and the concept of attenuating exponential in the process of ray tracing.The preferable visual effect has been obtained by setting up a non-refraction transparence model according to the characteristics of the fabric,using the ray tracing technique to simulate the reflection,transmission and shadow of the fabric surface,and applying such techniques as scene sculpt, illumination calculation,texture,anti-deformation,etc.