Abstract: Because it is necessary to use stable foam in mine fire extinguishing and preventing work, the reasonable control of the viscosity of base fluid can give full play to the fire extinguishing and preventing performance of foam. In order to study the effect of base liquid viscosity on the foaming performance and stability of mine-used fire-extinguishing foam, the effect of viscosity on foaming property and stability of foam was studied by experiments of rotating viscosimeter and Waring Blender method. The results show that the foaming ability can be improved by increasing the viscosity of base fluid within a certain range, but the foaming ability can be inhibited when the viscosity exceeds a certain range. It is also found that increasing the viscosity of base fluid can increase the apparent viscosity of foam and greatly improve the stability of foam.