The work aims to improve the conductivity of the electrode in the screen printing flexible sensor, and provide a reference for improving the electrical properties of the flexible sensor. Firstly, the molecular dynamic (MD) simulation method was used to establish the molecular dynamics model of conductive silver paste spreading on the surface of polyethylene terephthalate (PET) under different roughness factors in Wenzel model. Secondly, the binding energy of each system was calculated to characterize the binding ability of PET surface to conductive silver paste clusters in different systems. Then, the effect of the binding ability of silver paste and PET with different roughness factors on the conductivity of sensor electrode was explored by screen printing experiment. The simulation results showed that the conductive silver paste fell into the depression of rough surface during the spreading on PET surface with different roughness factors, and the binding energy between conductive silver paste and substrate increased with the increase of PET roughness factors. According to the experimental results, the conductivity of the electrode was significantly improved by PET with different roughness factors as the substrate. Compared with untreated PET, with the increase of roughness factor, the conductivity of conductive lines gradually increased by 77%, the resistivity gradually decreased by 43%, and the block resistance gradually decreased by 38%. Conductive silver paste will penetrate into the depression of the substrate during the spreading on rough surface, which increases the adsorption point, making the combination of silver paste and substrate closer, narrowing the distance between silver particles and enhancing the conductivity. Therefore, in order to increase the conductivity of the conductive lines, the roughness of the substrate can be appropriately increased.