Abstract: In Xiaqiao coal mine of Xuzhou Mining Group a large amount of water inflow from each level causes substantive expenses for drainage.Therefore,to save the drainage expenses,an under mine storage-drainage system is proposed to optimize the periods of drainage utilizing the electricity price difference between different periods.The calculation methods for underground pre-treatment including the calculation method for the number of probing and drainage holes and the hydraulics method are put forward based on the simple introduction of the under mine storage-drainage system.After two methods are compared and analyzed,it is found that the hydraulics method is closer to the drainage fact whereas the safe superfluity is not considered,and the calculation method for the number of probing and drainage holes is relative sketchy while the security coefficient is bigger.On application,two methods should be mutually validated and taking safe factors into account to make choice.