Abstract: Elastomer sealing performance is of critical importance for downhole tools application including the use of fracturing (Frac) plugs during multi-stage hydraulic fracking. In practice sealing performances of such plugs are normally evaluated through pressure tests, and in numerical simulation studies, maximum contact stress, average contact stress and contact length data are used to determine sealing quality between a packer and casing. In previous studies, the impact of friction forces on sealing performance is often overlooked. This work aims to fill this knowledge gap in determining the influence of friction forces on elastomer packer sealing performances. We first determined the most appropriate constitutive hyperelastic model for the elastomers used in frac plug. Then we compared analytical calculation results with Finite Element Analysis simulation using a simplified tubular geometry and showed the significant influences on interfacial friction on elastomer packer stress distribution, deformation, and contact stress after setting. With the demonstration of validity of FEA method, we conducted systematic numerical simulation studies to show how the interfacial friction coefficients can affect the maximum contact stress, average contact stress, contact stress distribution, and maximum mises stress for an actual packer used in plug products. In addition, we also demonstrated how the groove in a packer can affect packer deformation and evolvement during setting with the consideration of interfacial stress. This study underscores the critical role that friction forces play in Frac plug performance and provides a new dimension for optimizing packer design by controlling interfacial interactions at the packer contact surfaces.