Abstract: In this paper, the start-up behavior of cooper-water heat pipe heat spreaders in low temperature environment is investigated for airborne electronics cooling purpose. Low temperature environment condition is simulated using low temperature box. The effects of different cooling methods, different heat loads on heat pipe start-up performance in low temperature are analyzed by experimental study. The start-up temperature curves are obtained. In -55 ℃ environment, the heat pipe starts up normally under both liquid cooling (inlet liquid temperature is 10 ℃) and natural heat dissipation conditions. The start-up failure problem caused by low temperature at condensing section of heat pipe is not found.