Based on the design equilibrium of a fusion-reactor-level device, this paper systematically investigates the active control mechanism of edge localized modes (ELMs) via electron cyclotron wave (ECW) injection through comprehensive numerical simulations. A three-field reduced magnetohydrodynamic (MHD) model within the BOUT++ framework is employed, coupled with ray-tracing calculations from the GENRAY code, to simulate the localized deposition characteristics of ECW in the pedestal region and its subsequent impact on the stability of peeling-ballooning (P–B) modes. The simulations are performed under reactor-relevant plasma parameters, with ECW power deposition profiles systematically varied across the pedestal to assess their influence on ELM dynamics. The results show that the ECW deposition location plays a decisive role in ELM control. Specifically, mid-pedestal deposition enhances P–B mode instability and increases ELM energy loss, whereas deposition at the bottom of pedestal effectively mitigates ELMs. In this process, ECW-induced pressure perturbation is identified as the dominant factor influencing P–B mode stability. Furthermore, the plasma resistivity is found to significantly modulate the effectiveness of ECW control, exhibiting a strong coupling with the deposition location. For mid-pedestal deposition, the mitigation effect shows a clear resistivity dependence: under low-resistivity conditions, ECW injection effectively suppresses ELMs, whereas under high-resistivity conditions, it exacerbates ELM instability, leading to increased energy loss. This occurs because pressure perturbations induced by mid-pedestal deposition reshape the pedestal structure: at low resistivity, a narrower, steeper local pedestal forms that limits the crash width, while at high resistivity, the inherently stronger P–B mode instability causes multiple crash regions to develop, enlarging the overall energy loss. These findings highlight that the effectiveness of ECW-based ELM control depends on the synergistic interplay of deposition location and plasma parameters. This study provides important theoretical insights and optimization strategies for ECW-based ELM control in large-scale fusion devices.