MSC Classification: 35R35; 76F10; 78M35 In this work, we consider a mathematical model of an incompressible fluid governed by the generalized Stokes system in a stationary regime in a 3-dimensional thin domain Ω with Tresca friction law. The problem statement and variational formulation of the problem are formulated. Then the estimates on velocity and pressure are proved in a fixed domain. Finally, our main goal concerns the specific Reynolds equation and the uniqueness of the solution (û ,̂) are obtained. KEYWORDS a priori estimates, Reynolds equation, Stokes systems, Tresca law, variational formulationHowever, in this case, the Stokes principle is not satisfied.These types of models were studied intensively in the 1980s and 1990s by Necas et al, 8 in which the authors studied the particular types of fluids, and describe the shear thickening (p > 2) and shear thinning (p < 2) phenomena. The author in other works 9,10 establish regularity results up to the boundary for solutions to generalized Stokes and Navier-Stokes systems of equations in the stationary and evolutive cases. The asymptotic analysis of the type (1), in a thin domain with Tresca and Coulomb friction has been studied in previous works. 11,12 In Boukrouche and EL Mir, 13 the authors proved the asymptotic analysis of a non-Newtonian and incompressible fluid with stress tensor (u , ) = |D(u )| −2 D(u ) − I, in a thin domain. In Bayada et al, 14 the authors consider the Navier-Stokes equations in a thin moving boundary domain.