The system is made by the connection of broadband amplifier OPA847, current-feedback operational amplifier OPA695, attenuation network, filter circuit and MCU gain control module. In the first stage, the system can achieve 2 times fixed-gain by OPA847. Then, in the intermediate stage, it is made by the connection of two OPA847 to achieve 5 times gain. in the latter part, the system achieves 21 similar to 100V//V gain variation by OPA695 and T attenuation network. In the last stage, the system achieves the gain reduction by the high-pass filter network, AT89C52 is used to control the gain adjustment of this system, as well as the real-time display of the present output voltage gain. The range of the gain is 12dB similar to 40dB, changed by 4dB step-by-step. After testing, the whole system has stable performance and good control.