Abstract: Particle trap is the main method to suppress the movement of metal particles in direct-current gas insulated line (DC GIL). Optimizing the structure parameters can improve the effect of particle trap. In this paper, the dynamic model of particle motion was first established, and the mechanism of trapping particles was analyzed. Then, the characteristic value of electric field affecting the capture effect was obtained. Furthermore, the influence of trap structure parameters on the characteristic value of electric field was studied. Finally, the parameters of the particle trap were optimized based on the whale optimization algorithm (WOA), and the feasibility of the optimization was verified by experiments. The results show that the electric field strength at the bottom of the trap decreases with the slot width decrease, and when the trap's thickness and number of slots increase, the electric field strength at the bottom of the trap also decreases. When the ratio of the trap's thickness to the inner diameter of the cavity is greater than 0.16 and the number of slots is greater than 15, the electric field strength at the bottom of the trap tends to be saturated gradually. When the ratio of the trap's thickness to the inner diameter of the cavity is less than 0.20, the axial electric field in front of the trap increases with the trap's thickness. Besides, after the collision of particles with the high voltage electrode, the electric field force and electrical gradient force towards to the trap are the key factors for trapping particles. As the trap thickness increases, the the particle capture effect will be improved.