The present invention discloses a curved gate automatic switch. It includes water storage cavity, frame, pulley, gate, steel rope and automatic contraction device connected with steel rope. On the frame, a jack horizontal starting switch is set, the inner side of said gate is equipped with an operation door. It is characterized by that on the frame a lever starting machine and a gear are set, saidlever starting machine is connected with gate by means of steel rope, on the operation door of inner side of said gate a multi-bar mechanism is mounted, and said multi-bar mechanism is connected withsteel rope and automatic contraction device. Said invention also provides the working principle of said curved gate automatic switch and its concrete operation method. Said invention can attain the goal of automatically and safely discharging flood.