A kind of stainless-steel heat pipe with sintered fiber wick is investigated with the aim to improve the heat dissipation when it is used in spent fuel pools in nuclear power plants. The effects of test angle, porosity, and the filling rate on the heat transfer performance of the heat pipe are studied. At a test angle of 90 deg, the permeability plays an important role in the power limit since gravity can provide the necessary driving force. Larger porosity involves poor heat conductivity although it results in better permeability. When the test angle is zero, gravity is no longer the driving force. In this case, the evaporation section can still avoid dry burning because part of the evaporation section is dipped in deionized water. Therefore, permeability and filling ratio are two important factors influencing the power limit. Filling rate determines the vapor-flowing space. When the test angle is smaller than zero, gravity becomes a resistance force. Then, the lag tension and the filling rate exert the greatest influence on the performance of the heat pipe. Smaller porosity corresponds to a smaller contact angle.