When the inter-turn short-circuit transpires in the reactor, a high-frequency oscillation short-circuit current will be excited in the line, which will induce local overheating. Accurately grasping the temperature rise characteristics in the affected region has become a crucial means for enhancing ability of fault diagnosis and early warning. For the purpose of investigating the thermal response of the reactor under different positions and varying severity of inter-turn faults, a 2-D magnetic-fluid-thermal coupling model of a dry-type air-core reactor is developed by using a multi-physical field analysis method. The presented model integrates magnetic flux analysis with convective heat transfer computations and turbulent flow simulations. Firstly, the accuracy of the model is verified by comparing the simulated current and inductance with the experimental data. Then, the inter-turn short circuit scenes under different positions as well as varying severity are simulated, the magnetic and temperature-flow fields are coupled in two directions, and the temperature variation characteristics of the reactor in various scenarios are obtained. The research shows that under normal operation, the reactor’s temperature distribution generally presents a trend of high before and low after, high inside and low outside, and the highest temperature is 62.7 °C. In the situation where an inter-turn short circuit takes place, the temperature of the fault area will rise sharply. As the severity of the short-circuit intensifies, that is, there will be a linear upward trend in both the amplitude of temperature rise and the count of short-circuited turns.