The invention relates to a method for identifying a flaw of a steel plate. The method comprises the steps of processing an ultrasonic echo signal to obtain a wave curve, intercepting the wave curve to acquire a flaw wave curve, calculating the wave curve to extract peak data to obtain a flaw-type data group, further processing the flaw-type data group, and finally acquiring the flaw type of the steel plate by utilizing a flaw threshold value judging method and a morphology analysis method. According to the method for identifying the flaw of the steel plate, the flaw of the steel plate can be identified only according to the echo signal acquired by an ultrasonic probe device, the calculation speed is high, rapidness and accuracy in identification can be realized, a great amount of sample data is not needed for training, the data calculation amount is reduced, the identification speed is increased, and the flaw identification cost is reduced.