Abstract: In this paper,the pool boiling heat transfer characteristics of a machined porous surface tube are investigated experimentally,considering the boiling operating condition of passive residual heat removal exchanger.The experiments have been carried out with high-pressure saturated steam condensation in tube as heating source and the results show that the porous surface tube has a considerable boiling heat transfer enhancing ability: the porous surface tube can increase the boiling heat transfer coefficient about 68%~75% and the wall superheat decreases about 1.5℃;With the combined effect of condensation inside tube and boiling outside tube,the axial wall temperatures of heat transfer tube are neither uniform nor linear distribution,but represent some particular distribution characteristics.On the base of the experimental investigation,the enhanced mechanism of porous surface tube is also analyzed.