Abstract: Coal seam mining destroys aquifers,resulting in a large loss of water resources,and it is of great significance to implement water conservation during mining. Quantitative calculation of water loss in protected aquifer is the bottle- neck of water-conserving mining theory at present. Based on the results of numerical simulation of overburden failure in yushen mining area of northern Shaanxi Province,the process of roof water loss with mining is divided into two modes,one is the single weathered bedrock water-filling model,the other is composite water-filling model of Sarawusu Forma- tion and weathered bedrock. Based on the system dynamics theory,we proposed the double-exponential decay model to describe the water loss modes,established the mathematical relationship of water loss process with actual drainage and without drainage,and calculate the approximate solution of model parameters with physical meaning determined by McLaughlin formula,as well as the water loss process with peak value and equilibrium value,and their occurring loca- tion. In addition,we simulated the flow process in mining disturbance area by Comsol Multiphysics,calculated the in- tensity of water loss per unit strike distance. The results indicated that,overburden combination characteristics control the multiple release process of dynamic and static reserves of roof aquifer in mining,and determine the water loss mode,when compared with the two water loss modes,the peak value and dynamic equilibrium value of water loss under the combined mode are larger,drilling water drainage significantly reduces the peak intensity of water loss during min- ing,changes the mode and timing of water loss of roof aquifer,but cannot change the dynamic equilibrium value of wa- ter loss and the total amount of water loss during mining,the calculation results of total water resources loss and pro- portion of loose layer and weathered bedrock water in water resources loss intensity,indicate the protective effect of Pa- leogene clay aquifer on phreatic water storaged in Salawusu Formation. The conclusion provides a new way for the quantitative calculation of water loss and protection of aquifer at working face scale.