According to the surface micro-element bidirectional reflectance distribution function (BRDF), the polarization effect of the object’s surface is analysed. Based on infrared polarization characteristics in long wave band, a model combining the infrared reflected effect and emitted effect is developed to calculate the polarization degree. The simulation result of this model indicates that the degree of polarization is determined by the value of the ratio of emitted radiation to reflected radiation. With the use of RadThermIR, the emitted radiation and reflected radiation of the sea surface and ship targets can be obtained. Based on radiation results and the proposed polarization calculation model, the polarization degree of the ship and sea water surface in different time and different detected angle is simulated. Experiments were conducted to measure the polarization degree in sea scenarios. The experimental data are consistent with the simulated results, which validates the effectiveness of the proposed model.