The invention relates to a variable gain mixed-frequency amplifier and a biological signal acquisition and processing chip and system. The chip comprises the variable gain mixed-frequency amplifier 11, a local oscillation signal generation circuit 12, an energy acquisition unit 13, a first capacitor C1 and a first resistor R1; a biological signal input end Vin of the variable gain mixed-frequency amplifier 11 receives biological signals, a power supply output end VDD of the variable gain mixed-frequency amplifier 11 is electrically connected to the energy acquisition unit 13, a local oscillation signal input end LO of the variable gain mixed-frequency amplifier 11 is electrically connected to the local oscillation signal generation circuit 12, a grounding end GND of the variable gain mixed-frequency amplifier 11 is used for obtaining external ground-supplying signals, and an output end Vout of the variable gain mixed-frequency amplifier 11 is electrically connected to a first end of the first capacitor C1 and a second end of the first capacitor C1 for outputting modulated audio signals; the local oscillation signal generation circuit 12 is used for receiving alternating current signals and supplying local oscillation signals to the variable gain mixed-frequency amplifier 11 after processing; the energy acquisition unit 13 is used for receiving the alternating current signals and supplying direct current power to the variable gain mixed-frequency amplifier 11 after processing.