Abstract: For lightening or improving reliability and security,more and more space aircrafts with short periodic missions need to evacuate the working fluid after the mission ending. Based on the two phase flow and the liquid flashing vaporization theory,together with the N(C₂ F₅) ₃ flashing vaporization experiment carrying out in the pressure rapidly decreased surrounding,it was analyzed in the present study that the working fluid N(C₂ F₅) ₃ in the fluid loop evacuating in high vacuum under 1/6g gravity and condition. The results indicated that the N(C₂ F₅) ₃ evacuating in the high vacuum would tempestuously flash vaporization. The time of working fluid evacuating was decided by the Pressure Evacuating Stage,the Gravity Assisted Evacuating Stage and the Flashing Vaporization Wave Transmitting Stage,and only the second stage depended on the gravity,the last stage time is the longest. The velocity 0.23m/s of the flashing vaporization wave transmitting was experimentally measured in the plastic pipe with 9mm in diameter. It was faster than the prediction by Simes-Moreira & Shepherd simplified model.