A flap type rudder for saury boats comprises a stern, a rudder shaft, a shaft sleeve, a main rudder, a revolving shaft, an auxiliary rudder, shaft caps, a revolving shaft sleeve, a sliding shaft and a connecting rod, and is characterized in that the rudder shaft is installed on the stern through the shaft sleeve, the main rudder is installed on the lower portion of the rudder shaft, the main rudder is connected to the auxiliary rudder through the revolving shaft, the sliding shaft is arranged on the upper portion of the auxiliary rudder, the sliding shaft is installed in the revolving shaft sleeve, the shaft caps are installed at the upper end and the lower end of the revolving shaft sleeve, and the shaft caps are fixed in the shaft sleeve through the connecting rod. The flap type rudder for the saury boats is high in work efficiency and wide in market prospect.