Earth sensors are widely used in spacecraft for attitude determination. They need to have a very large field of view (FOV) (>120°) and relatively low accuracy while being used in the aircrafts around orbit. A triple-FOV infrared earth sensor is proposed in this paper. It uses three pieces of standard infrared detectors with a wavelength range of 14 ~ 16μm, to sense the horizontal circle by detecting the infrared light emitted from the earth. From which, the geocentric vector can be obtained. A mathematic model is established and a validation model is set up to provide input parameters for the mathematic model. The simulation results of the two models show that the output of the mathematic model coincides with the known parameters. Based on the above analysis, a prototype has been built and tested. The test results show that the angle measurement error is about 0.002° and hence such a triple-FOV earth sensor is capable to provide high-precision position information for autonomous navigation.