In recent years，the technology of IR polarization imaging has developed rapidly. However，research on the mechanism of polarization has just begun. In order to study the generation of IR polarization and related influencing factors，a polarization model based on complex refractive index is proposed. The model is to describe the polarization properties of air-smooth media surface and can be applied to both absorbent and nonabsorbent media. In this model，observing angle is the input and the complex refractive index of the media is the parameter which can be changed according to the material. The outputs include the reflectivity and the emissivity of the perpendicular and parallel components. Also，the model can output the degree of polarization when only reflection or emission exists. Based on the polarization model，a series of simulation is made in MATLAB and the generating mechanism of polarization of reflection and emission is studied deeply. Also，using this model，this paper describes how reflection and emission influence the polarization of targets. The polarization model can help us understand IR polarization better and provide theoretical support for polarization detection.