In this paper, a fluid-thermal coupled finite element model is established based on the design parameters of dry-type core reactor, the detailed temperature distribution results are given, and the heat transfer process of the layer coils was analyzed. Meanwhile, the electromagnetic characteristics of core reactor have been analyzed, it shows that the structure parameters adjustment of layer coils have little effect on the inductance of reactor. Taking the metal conductor usage of coils as the optimization object, the heat dissipation process between the layer coils and air ducts is equivalent to the vertical pipe, the calculation method of temperature rise is given, and the thermal efficiency optimization method of dry-type core reactor is proposed based on the particle swarm optimization algorithm, which can obtain the optimal structure parameters of coils. According to the optimization design results, the metal conductor usage of coils is only 80% compared with the initial parameters, and the correctness is verified by the simulation results. Thus, the optimization method can significantly improve the thermal efficiency and reduce the metal conductor usage of core reactor.