The invention discloses a low-noise analog front end for an asthma monitor. The low-noise analog front end comprises an active low-frequency second-order filter, a low-frequency LNA (low-noise amplifier), a PGA (programmable gain amplifier), an ADC (analog-digital converter) and an MCU (microprogrammed control unit); after expiration of an asthmatic patient, expiration flow signals are converted into voltage signals through a pressure sensor, the signals filtered by the active low-frequency second-order filter are transmitted to the LNA, the LNA amplifies the filtered signals preliminarily onthe premise of low noise and transmits the signals to the PGA, the PGA performs sectional programmable amplification on the received signals according to different flow ranges, the amplification timesof the PGA is controlled by the MCU, the signals after the sectional programmable amplification are subjected to analog-digital conversion by the ADC and output to the MCU, and after MCU processing,a result is output in a form of audible-visible alarm. By means of sectional programmable amplification of the flow signals by the low-noise analog front end, the resolution ratio of the asthma monitor in a low-flow range is increased effectively.