The malfunction of SPD can incur many problems. The most hazardous problem is the fire and explosion resulted from the failure of MOV (Metal Oxide Varistor). The reasons for the fire are analyzed and the working mechanisms of thermal fuses are described. The method using thermal fuses to protect SPDs from excessive heating and MOV fire is introduced. In order to test the characteristics of thermal fuses, the tolerance impulse overcurrent, the voltage limiting, and thermal stability experiments are designed. The results indicate that using a thermal fuse as the arrester disconnector can stand the impulses of thunders. The change rate of the residual voltage is only 22% and the switching voltage is within 10% after the experiment. It shows that thermal fuses do not affect the voltage limiting performance of MOV. When the MOV is over heating, the thermal fuse can rapidly blow out and turn off the circuit to inhibit current to protect working systems. Comparison is conducted between thermal fuse and low temperature soldering tin through thermal stability experiments. It is discovered that thermal fuses have certain advantages when the operating temperature is blow 130 ℃.