A front-end circuit for uncooled diode infrared detector, composed of Gm-C-OP integrated amplifier, was designed. The small input voltage steered from diode detector was transferred into current by an operational transconductance amplifier(OTA), and then the current was converted to voltage by a capacitor transimpedance amplifier(CTIA). The OTA used a current feedback loop to achieve higher linearity and transconductance than the traditional one. By adopting differential input structure, Gm-C-OP integrated amplifier can eliminate the effect of ambient temperature and process on the output signal of detectors. The circuit was fabricated in a 0.35 μm CMOS process under 5 V supply voltage. The Gm-C-OP integrated amplifier occupies an area of 0.012 6 mm2. The input differential voltage varied from 0 to 5 mV. Testing results show that the transconductance of OTA is in accordance with the simulation results. The Gm-C-OP integrated amplifier can convert the dynamic small input voltage into a proper voltage linearly and the linearity is 97%. The output range exceeds 2 V.