In order to realize the combined detection of steel plate before and after corrosion and shock vibration state ,an ultrasonic detection system based on fiber Bragg grating ( FBG) was constructed. Firstly ,the demodulation principle of fiber grating based on tunable laser light source is analyzed theoretically. On this basis ,the variation law of Lamb wave signal before and after steel plate corrosion was studied experimentally ,and the time-frequency variation characteristics of steel plate impacted with different vertical impact intensity and the time-frequency variation charac- teristics of impact vibration signal before and after steel plate corrosion were analyzed. The research shows that the fi- ber Bragg grating ultrasonic detection system built can effectively realize the combined detection of steel plate corrosion and shock vibration signals ,and can accurately identify the corrosion of steel plates through the amplitude of the Lamb wave signal and whether there are new frequency components. There is a linear relationship between the amplitude change of the shock signal and the size of the shock. At the same time ,the frequency domain analysis proves that the frequency components of the corroded steel plate shift to the right by an average of 12 Hz.