Provided is a multi-band audio frequency sonar grass bream trapping frequency modulator. The output ends of a group of audio frequency oscillating coils are in series connection with sonar capacitors, wherein the number of the output ends is two. A group of sonar control coils comprises two symmetric coils, wherein a central tap of the sonar control coils is connected with the negative electrode of a power supply and the emitting electrodes of two groups of sound wave triodes jointly through resistors, and the other two ends of the sonar control coils are connected with the base electrodes of triodes respectively through diodes. A group of sound wave power coils comprises two symmetric coils, wherein a central tap of the sound wave power coils is connected with the positive electrode of the power supply through a shunt resistor of an ampere meter and a switch, one end of the sound wave power coils is connected with the collector electrode of one group of sound wave triodes, and the other end of the sound wave power coils is connected with the collector electrode of the other group of sound wave triodes before being grounded. A voltmeter is in parallel connection to the input end of the power supply, and the ampere meter is in parallel connection to the shunt resistor.