In simulating section dyed yarn, how to achieve the transition between two colors is the core. In this paper, we finish it by using the linear interpolation and the cubic spline interpolation in numerical analysis to establish the basic color gradient model. Then, taking the 2 colors and 3 colors-sections dyed yarns for example, we combine the existing yarn model with the color gradient model in the paper, in the way of texture synthesis to achieve the simulation of section dyed Yarn. At last, based on the specific process parameters in dyeing process, we optimize the established model to make it more practical and more widely.