Abstract: In underwater ordnanac,the underwater acoustic amplifier handles an exceptionally wide range of input signal levels,by using Automatic Gain Control(AGC),which not only is a significant part of am-plifier,but also is the necessary key equipment. The VCA610 is a wideband,continuously variable voltage controlled gain amplifier,with the features of low noise,high input impedance,and wide bandwidth. E-specially It provides linear-dB gain with a control range of 80dB. Based on its features and specifica-tions,analyzing the VCA610′s Input/Output relation,the VCA610 has been applied to AGC circuit of un-derwater acoustic signals,with a constant output for the input range of 60dB. And an offset adjustment for the control circuit of VCA610 in the amplifier is designed.