This study examines the impact of magnetic hyperthermia on treating peritoneal metastasis and analyzes the effect of coil geometry. The aim is to evaluate the efficacy of localized heating in eliminating cancer cells while preserving healthy tissue, with a specific focus on the influence of coil geometry on magnetic nanoparticle hyperthermia for treating peritoneal metastasis. Magnetic nanoparticles concentrate heat within the tumor, minimizing damage to surrounding tissues. Magnetic nanoparticles Fe₃O₄ were used to raise tumor temperatures to 42–46°C under an alternating magnetic field. A numerical simulation based on the finite element method was conducted to assess the effects of coil geometry and tumor location on heat transfer. The magnetic field distribution was calculated using Maxwell’s equations, while heat generation by nanoparticles was determined through Rosensweig’s theory. The Pennes bio-heat transfer equation was then applied to evaluate temperature distribution in both tumor and healthy tissues. The findings indicate that coil geometry significantly affects the distribution of the magnetic field, heat, and temperature. Cylindrical, flat, conical, and inverted conical coils generate the lowest overall heat while ensuring even distribution, leading to minimal temperature variations across the tumor. Therefore, these coils produce a more uniform temperature distribution within gastric tumors and peritoneal metastases. Additionally, they achieve the therapeutic temperature range required for cancer treatment. The temperature in healthy tissue remains around 37°C, confirming the absence of damage. Therefore, the aforementioned coils are the most suitable for use in magnetic hyperthermia as a treatment for gastric cancer and peritoneal metastasis.