While flexible electronics are ready for the market, keeping their good electric conductivity in long-term operation is still one of the inevitable challenges. This paper aims to develop a resistance degradation model based on the analysis of the observed fatigue behaviour of thin films and the premature electric failure of thin films. The material deterioration process due to fatigue is represented by the defined fatigue damage variation based on cracks initiation and growth, which establishes a connective relationship with electric resistance degradation. The developed model is validated to compare with experimental results, and numerical results show that it can accurately predict the fatigue life and electrical resistance degradation of thin films of different thicknesses; therefore, it could be a means to assess the electrical performance of thin films on flexible substrates.