The invention discloses a band-gap reference voltage source. The band-gap reference voltage source comprises a level switching circuit, a first field-effect tube, a second field-effect tube, a third field-effect tube, a first audion, a second audion, a third audion, a first resistor, a second resistor and a clamping circuit. The level switching circuit is used for generating identical first-order positive temperature coefficient voltage at the first end and the second end according to voltage input at the input end. According to the band-gap reference voltage source, the identical positive temperature coefficient voltage is introduced to a drain electrode of MP1 and a drain electrode of MP2, the channel length modulation effect of MP1 and MP2 is used for eliminating or reducing the second-order temperature coefficient, and therefore second-order temperature coefficient compensation is achieved.