An online evaluation method for electrical contact reliability of in-service aircraft based on infrared characteristics is proposed. The long-term vibration, corrosion, high temperature and other environmental loads of in-service aircraft lead to the deterioration of the surface condition of the electrical contact carrier, and its degree is often difficult to quantitatively evaluate. Firstly, it is found that the spotty characteristics cause the decrease of contact resistance and other reliability indexes through model mechanism analysis. Then a certain torque load spectrum is applied to a certain type of electric contact carrier, so as to obtain the "thermal" information of the electric contact part in real time. Under the condition of low load and near rated load, the speckle characteristics appear obviously with the change of load state. It is concluded that the maximum temperature in the area of thermal contraction line, the density of isotherms, the area of connected region and the degree of boundary blurring as the characterization indexes can reflect the actual attenuation degree of mechanical load applied on electrical contact surfaces. So it can be used as an effective evaluation method for the deterioration degree of contact resistance of aircraft in service.