This paper proposes a methodology for efficient multiscale modeling and simulation of washcoated microchannel reactor by the use of an effectiveness factor submodel. The methodology is demonstrated in the context of modeling a microchannel methane reformer for miniaturized gas-to-liquids (GTL) application. The effectiveness factor submodel is derived specifically for a detailed multi-step reforming kinetics using the data provided by 2D CFD simulations with simplified reactor geometry and fully resolved washcoat. The generalized Thiele modulus approach is exploited to facilitate simple explicit estimations of the effectiveness factors of CH4 and H2O. The root mean squared error of the predictions is shown to be 0.015. On this basis, a hybrid model is formed including the CFD model of the reactor, 1D reaction diffusion equations of the washcoat and the effectiveness factor submodel as the interface in-between. The hybrid model Can accurately reproduce gas phase and intra-washcoat profiles of gas species and surface reaction intermediates for various washcoat properties along with time savings of more than an order of magnitude. The results also show that the reformer's performance is sensitive to washcoat diffusion resistance. (C) 2017 Elsevier B.V. All rights reserved.