An improved model for the motion dynamics of a metallic particle located in the non-uniform electric field area in the gas insulated system is proposed. To represent the special area, a diverging conducting electrode is used in this study. Based on the fluid mechanics theory, the forces imposed on metallic particle are first developed. The motion process is then divided into two modes, i.e. the particle rolls on the electrode surface and moves in the gap. The collision and reflection processes between the particle and the electrode are crucial to the motion, and they are fully considered in the proposed model. The trajectory of the particle under different voltages is obtained. The evolution of metallic particle is divided into four stages, and it is featured by four quantities, i.e. the critical jumping point, the minimum horizontal position, the falling point, and the motion time. The characteristics for each stage are analysed, and the sensitivity analysis of the quantities are performed. The impacts of the applied voltage, the particle radius, the initial position etc. are discussed. The results provide guidance for particle trap design.