According to the characteristics of the UV communication signals in free space near surface layer, based on the modulation methods of UV signals, the frequency-choosing characteristics and specifications of ampli. fiers are proposed. Based on the predetermined specifications, frequency-choosing circuits and three -level amplifi. cation circuits are designed. The overall characteristic curves can meet the requirements of actual application for gains modulation circuits, which can perform gain compensation and gain trimming. The simulation results by Multi. sim shows that: the amplifier has continuously adjustable gains magnification between 10 000～100 000 at the cen. ter frequency of 30 kHz and 50 kHz. And the bandwidth near center frequency is about 2 kHz, the equivalent input noise voltage is ≤ 5 nV/Hz @30 kHz、50 kHz. The amplifier is more suitable for magnifying weak UV signals near surface layer for using low-noise apparatus, which provides certain reference value for actual application.