The current invention discloses a flood barrier having a first compartment and a second compartment, both compartments being preferably in an elongated shape from a side sectional view and being parallel in position. The flood barrier also includes a blocking membrane disposed in the second compartment, wherein a bottom end of the blocking membrane is attached to the bottom of the second compartment and a top end of the blocking membrane is attached to a floating member. The flood barrier may be positioned in the ground in front of a building, wherein when flood water approaches, the floating member may be kept afloat and pull the blocking membrane upward to block the invasion of flood water.