The accumulation of heavy metals in mushrooms has presented a significant risk to human health, underscoring the importance of devising a portable and cost-effective method for detecting heavy metals. Thus, we have developed an electrochemical sensor based on 3-dimensional highly reduced graphene oxide (3D-HRGO) in conjunction with Fe₃O₄ nanoparticles, enabling the simultaneous quantification of Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺. The 3D-HRGO/Fe₃O₄ nano-particles material prepared in this study was characterized and confirmed by multiple techniques, then dispersed in a simple and environmental dispersant, consist of 75% ethanol and 0.1% Nafion, and coating on a glass carbon electrode (GCE) to preparing a 3D-HRGO/Fe₃O₄/GCE sensor. The limit of detection (LOD) of 3D-HRGO/Fe₃O₄/GCE sensor for Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺ in simultaneous detection were 0.2 μg/L, 0.6 μg/L, 0.6 μg/L, and 0.9 μg/L, respectively. The sensor demonstrates exceptional stability, reproducibility, anti-interference, and recovery rate. Furthermore, the electrochemical sensor was employed to detect heavy metals in actual mushrooms and validated through conventional methodologies. This study represents the pioneering utilization of 3D-HRGO/Fe₃O₄ as a foundational material for an electrochemical sensor capable of simultaneous detection of multiple metals, thereby advancing the progress of on-site and expeditious detection techniques.