Delta robot is a kind of parallel robot that is widely used in industrial applications for its impressive advantages compared to the serial robot such as fast-moving speed and great productivity assembly. It is very useful for classification products and assembly requiring high processing speed. Saving materials and costs during the design and manufacturing process while ensuring the working capabilities of robots such as stiffness and durability is very important. Therefore, the authors propose an approach of utilizing the topology optimization method in the design process to solve such a problem. In this paper, the process of studying and applying the topology optimization method to design the Delta robot arm is presented. The redesigned product has a lighter weight, consumes less material, and therefore has lower manufacturing costs but still ensures the mechanical properties and the working ability requirement.