Abstract: The system of water storage-drainage in abandoned roadway was established in the paper,it takes measures of impounding at peak of electricity costs and draining at valley of electricity costs in order to reduce expense of mine drainage.Based on previous research,formulas of water storage-drainage for area with gradient conduit shape were derived from hydraulic formula and mass conservation equation,drainage facilities were designed from security and economy.The conceptions of useless storage and useful storage of system were elicited.Eigenvalue of water storage-drainage under the conditions of gravity and different inflow were calculated.The change of water head,discharge,discharge proportion of storage from reservoir full to empty were analyzed.The results showed that,water head decreases linearly from maximum to minimum while draining from full-reservoir to empty-reservoir.Meanwhile,about half of storage has been drained at the first 1/3 time;then,80% of storage has been drained at the 2/3 time and discharge decreases linearly;at the last 1/3 time,discharge decreases quickly to water inflow and only 20% of storage is drained.