The separation of circulating tumor cells has attracted extensive research due to its critical role in cancer therapy, including diagnosis and prognosis. In this study, we introduce an advanced microfluidic device integrates dielectrophoresis configuration, to separate circulating tumor cells (CTCs) from blood constituents, which are white blood cells (WBCs) in particular. Our design incorporates a flow-focusing microfluidic chip with planar interdigitated electrodes embedded at the chip's bottom. A non-uniform electric field is generated between these electrodes, producing dielectrophoretic forces applied on cells. Hence, biological cells’ trajectories are directed in different paths which rely on their characteristics. Cells exhibiting similar features may migrate in an identical trajectory, enabling the separation of WBCs and CTCs. Finite element method was used to numerically analyze the novel design. This design has a potential with ease of fabrication, label-free and non-invasive manner, with a high-efficiency and purity.