The invention relates to an automatic coal gas anti-leakage device, which comprises a water sealing the with a overflow hole at its upper part and a float cylinder which can close the overflow hole when it is high; said float cylinder contains a core cylinder with a water outlet at upper part; the upper part of said core cylinder is connected to a vertical hollow guide rod through to the outer space of water sealing tube; said hollow guide rod is sliding matched with the water sealing tube; the lower open of said core cylinder is mounted with a horizontal valve plate which is connected to the vertical valve rod; and said valve rod and the hollow guide rod can form a motion couple. Compared with present hinge valve plate, the invention is more sensitive to the pressure of coal gas, with stable switch property and simple structure. |