In order to improve the design capacity of knitted fabric pattern and explore new design thought, this article studies the fractal image generation of Julia set and applies it into the pattern design of seamless underwear products. It adopts VB programming to generate Julia set pattern based on escape time algorithm, and then uses part imaging and amplification or changes the function orders to get a lot of colorful patterns. When these generated patterns are imported under the help of Photon software, color part in the patterns will be replaced with pre-designed fabric patterns and finally comes with patterns identifiable to seamless underwear knitting machine. Such method greatly expands the design thoughts of seamless underwear products.