The electrical characteristics of Silicon Photomultipliers(SiPMs) were analyzed on the basis of the behavior model of a micro plasma electron in the SiPMs, and an optimum design scheme for the SiPM front was proposed. The working principles of SiPM arrays were introduced, the electrical behavior model of a SiPM was given, and the advantage of SiPM for the underwater three-dimensional depth sounder was discussed. Based on the echoing characteristics of the underwater depth sounder, a high speed, high bandwidth preamplifier was designed, and an alternating current analysis and a transient analysis were performed. Results show that the preamplifier circuit has much high gain flatness in the bandwidth and the phase margin is more than 60°, which ensures the integrity of signals and the waveforms of laser pulse signals. Analysis and test results indicate that the SiPM arrays and the circuit design can satisfy the requirement of underwater three-dimensional depth sounder, and can improve the target acquisition performance of the laser underwater imaging systems.