The calculation of turbulent premixed flames in the framework of the Probability Density Function (PDF) approach remains quite a challenging modeling problem because of the strong coupling that exists between micromixing and reaction in premixed flamelets. In the flamelet regime of turbulent premixed combustion, instantaneous progress variable gradients are essentially fixed by these propagating flamelets. Consequently, the PDF evolution due to the micromixing term cannot be handled without taking into account the reactive contribution itself. In this study, a generalization of the work of Pope and Anand (1984; Flamelet and Distributed Combustion in Premixed Turbulent Flames, Proc. Combust. Inst., vol. 20, pp. 403-410) is put forward to take into account the consequence of flamelet structure, but only when and where this structure is not perturbed by turbulence. In this manner, a criterion based on the ratio of the Kolmogorov length scale eta(K) to laminar flame width delta(L) allows turbulent premixed combustion to be described with a unique model from flamelet to distributed combustion regime. The new unified model is applied to the propagation of one-dimensional turbulent premixed flame in prescribed turbulent flow conditions and to the case of a high-velocity piloted Bunsen burner.