Abstract: The gas drainage with boreholes is an important means to control coalmine gas. Borehole in underground coal mine is different to conventional geological drilling; moreover, performance requirements are stricter to flushing fluid. Flushing fluid should has characteristics: good instant solubility, dispersion ability, excellent ability of increasing viscosity, lubrication and inhibition. Additive for flushing fluid was developed and was compared with foreign product. Test results show that properties of additive developed were equivalent to foreign product. Additive developed can meet the requirements of flushing fluid.