This work proposed a novel necking heat pipe with double-end heating for thermal management of the overload operation. The addition of another heat load was adopted to obtain a higher threshold critical power for the heat pipe system. The thermal performance of thermal switch heat pipe (TSHP) and traditional grooved heat pipe (TGHP) was investigated experimentally, including the threshold critical power, starting characteristic, recovery characteristic, surface temperature distribution, thermal resistance, etc. The optimized TSHP exhibited a larger threshold critical power range with low additional heat load input (from 55 W to 65 W, almost 20% increase), low starting additional heat load input (2 W), good recovery characteristic (less than 150 s from 75 °C to normal after overload), and low thermal resistance with additional heat load input (less than 0.13 °C/W). These results indicate that the optimized TSHP can offer great potential for the overload operation situation with the additional heat load. Such a novel necking heat pipe with double-end heating can be utilized in heat pipe systems to obtain different thermal performances for complicated working situations, especially for the overload operation situation.