Electric vehicle (EV) participating in grid ancillary frequency regulation involves leveraging the "source-load" characteristics of EVs to quickly eliminate system frequency fluctuations. However, ensuring the economic feasibility of large-scale EV-assisted frequency regulation while maintaining system performance remains a challenge. To address this, a distributed economic model predictive control (DEMPC) method is proposed for large-scale EV aggregated charging stations assisting in grid load frequency control (LFC). Based on economic model predictive control, the DEMPC method employs a single-layer control structure to oversee a two-tiered hierarchical system, enabling distributed collaborative control across multiple regional power grids. The optimization of controllers is achieved through convex relaxation of the economic cost function. The collaborative work of each subsystem controller with adjacent subsystems ensures the control performance of the entire system, and an appropriate terminal cost function guarantees the asymptotic stability of the system. Simulation results demonstrate the effectiveness and superiority of this method.