To measure underwater acoustic signals with laser technology, the principle and hardware structure are presented, including photodetector circuit, pre-amplifier circuit, high-pass filter circuit, after-class amplifier circuit, low-pass filter circuit, notch filter circuit of 50 Hz, serial communication circuit, memory expansion circuit, etc. The control and calculating circuit are designed based on digital signal processor TMS320LF2407A, and virtual machines are used to achieve real-time display of signal detection. Experimental results show that the system can detect underwater acoustic signals well.