Magnetic interstitial hyperthermia is a hopeful treatment method for tumor. Before treatment, the tumor would be embedded with a number of ferromagnetic seeds, which can produce energy under an alternating magnetic field. The tumor cells would be necrosed once the temperature exceeding to a value. However, the normal tissue around the tumor is expected to be under safety. Hence, temperature simulation is necessary to avoid any mistake treatment planning, meanwhile, the calculation is required as quick as possible. We developed an efficient cellular automata (CA) numerical method to solve the bioheat transfer equation. The CA equation is derived from Lattice Boltzmann equation. As a discrete numerical method in space and time, CA can be used to deal with the complicated boundaries, such as the huge vessels incorporated in the tumor, which were not well treated in traditional methods. The model of ferromagnetic seed, which is critical to the numerical results, is treated with a simple numerical temperature model. In order to evaluate the proposed method, in vitro and in vivo experiments are carried out, respectively. After comparison between the numerical and the experimental results, the proposed method shows perfect calculation precision and high efficiency, which is significant for clinical treatment.