A novel two-channel atmospheric pressure measurement system with optical fiber was put forward.The system consists of a two-path fiber optical fiber displacement sensor and twin metallic membrane boxes with high precision. The displacement produced by air pressure was detected with the fiber sensor. The characteristic of the system is independent of the light source. The output parameter is independent of the light,and is only dependent on the structural parameters of the fiber sensor. The signal processing circuit of the system was designed. The signal processing circuit mainly includes signal pre-amplifier,narrowband BPF,RMS converting circuit,A/D and the MPU circuit. The output characteristic curve of the system was acquired,the measurement precision is ±0.1 hPa,and the resolution is less than 0.2 hPa under the structure of the fiber sensor.