Abstract: The power tolerance performance is a core indicator for the engineering application of high-power transmitting antennas. Aiming at the thermal management challenges of end-fire array antennas under high-power working conditions, a multi-physics collaborative analysis method of “simulation—test—correction” is employed in this paper. An end-fire array antenna is encapsulated by co-curing process, and its complex coupling structure with over 60 elements leads to low heat dissipation efficiency. The thermal simulation model is calibrated by the measured data of the antenna in a 30 °C anechoic chamber, and it is found that the matching resistors have an overheating risk in a 70 °C environment. An equivalent test platform is built based on the installation environment, and the severe working condition screening technology is used to determine that the operating point at a frequency of 5.6 GHz and a beam point position of 0° is the most severe working point. Through the temperature monitoring of the 30 min continuous power transmission test combined with simulation analysis, it is verified that the temperature of internal materials of the antenna is all lower than the temperature resistance threshold. The research shows that the power tolerance performance of the antenna is collaboratively affected by the transmission efficiency, packaging structure and heat dissipation environment, and optimizing the gain efficiency and forced air cooling design can significantly improve the thermal management performance. This study provides a complete test verification system for the engineering design of high-power antennas.