In this paper, the connection stiffness between a thin-walled Z-beam and a sandwich panel is investigated by means of laboratory experiment, analytical approach, and numerical simulation. The scheme of the conducted experiment refers to a double lap shear test. The two thicknesses of the sandwich panel (100 mm and 60 mm) and two groups of fasteners (four and three) were investigated. The laboratory tests allowed for the determination of the failure mechanisms and the prediction of the reliability of the restraint of the thin-walled beam, provided by sandwich panels. The assumed finite element model created in Abaqus/CAE consisted of solid finite elements (core layer of the sandwich panel, roller support) and shell finite elements (thin-walled beam, facings of the sandwich panel). The fasteners were modeled implicitly, i.e. using spring connectors. The stiffness of the spring connector was determined on the basis of the derived analytical expression and the laboratory test results. The kinematical response of the adopted finite element model was in agreement with the laboratory results. Such a model can be used to verify more complex finite element models with explicitly introduced fasteners.