为实时动态测量未知深度水下目标微弱后向散射信号，设计了一种新型的光电倍增管(PMT)选通变增益探测系统。采用给PMT外加选通和变增益纳秒电脉冲的方法，通过改变PMT光阴极与第一打拿极之间电势差，实现PMT选通；借助给PMT最后一个打拿极外加变增益高压脉冲改变PMT最后一个打拿极与前置打拿极间的电势差，实现PMT变增益。实验结果明：在选通和变增益脉冲到来时，阳极输出相应的脉冲信号，信号脉宽为40ns，脉冲幅值增大，证明该方法能够实现PMT选通和变增益。

A novel range-gated gain-control photomultiplier tube (PMT) detector system was designed in order to detect the backscattering signal under water dynamically in real time. The gating of PMT was realized with the method of adding the applied gating and gain-control nano-second pulse, and by changing the electric potential difference between the cathode and the first dynode. The gain control of PMT was complemented by the aid of adding the high voltage pulse to the last dynode of PMT to change the electric potential difference between the last dynode and front dynode. The experiment result shows that, when the gating and gain-control pulses come, the anode outputs the relevant pulse signal whose pulse-wide is 40 ns. It proves that this method can realize the gating and gain-control of PMT.