Abstract: In this paper, simulation of the water mist is carried out by the fire dynamics software (FDS) to study the fire extinguishing process in the airtight cabin of a manned spacecraft under microgravity conditions. It is found that the water mist at a certain angle would not only promote the proliferation of the smoke, but also make the fire fighting operation difficult, because the fresh air would promote the combustion process. The temperature and the concentration of the carbon monoxide in the process of putting out the cable fire are obtained. Analysis shows that the particle size of the water mist in the gravity environment should be controlled between 100 and 150μm, and the spray direction should be perpendicular to the plane where the fire happens.