The work objective is the scientific rationale of forming parameters of the surface layer of machine parts by diamond smoothing. The research complexity means, first of all, analytical analysis of all active physical factors in machining and, in particular, during diamond smoothing. Based on the known dependencies from the theory of plastic deformations of metals, theoretical dependences of the yield stress during machining are obtained, taking into account the deformation rate of the metal of the surface layer and its current temperature. Using the finite element method, a graphic picture of the stress-strain state of the surface layer during diamond smoothing of various structural materials is obtained. Dependences linking such parameters of the surface layer as the density of metal dislocations, its grit and energy state with the conditions of the diamond smoothing operation are given. Methods are proposed for providing the endurance limit by diamond smoothing according to a single-stage scheme, which implies specifying conditions for the diamond smoothing operation that directly provide a given target function - the fatigue limit. A passport of the "diamond smoothing" method is developed, taking into account the previous state of the treated surface.