The utility model discloses an automatic water drainage device used for gas drainage tube of coal mine, including water tank, first inlet tube, second inlet tube, intake pipe, first drain pipe, second drain pipe and body, second pneumatic valve and check valve are installed respectively to the inboard of intake pipe, the other fixed mounting of tip of first drain pipe and second drain pipe has first ring flange and second ring flange, the middle part of water tank is equipped with fixed spout, the outside of fixed spout is equipped with the ball groove, the ball inslot gathers there is the ball, the middle part both sides of body all are connected with the slider through the connecting block, slider and fixed spout sliding connection. The automation that should be used for the coal mine gas is drained the ware and has greatly been improved the slip efficiency of slider, avoids the body because of the long -time card phenomenon that leads to of using, has fine filter effect, and convenience of customers in time knows the condition in the first drain pipe, easy to assemble and dismantle.