Abstract: The basic assumption of formation test in composite dual?porosity reservoirs in vertical wells is that wells should be located in the center of the inner region of the reservoir. However, this assumption is hard to be realized during the actual well test. Eccentricity is used to describe well locations in the inner region of composite reservoirs, then an off?center well test model considering skin effect and wellbore storage is established for composite dual?porosity reservoirs. The line?source solution of the model is obtained on the basis of pointsource theory, superposition principles and Laplace transform, and the solution in the real space is acquired by Stehfest numerical inversion, based on which the typical pressure curves are further plotted and the influence of eccentricity on typical pressure curves is analyzed.The results show that the influence of eccentricity on the pressure performance of composite reservoirs is mainly embodied in the transition stage of radial flows between that in the inner region and the fracture system in the outer region. And a bigger eccentricity will lead to an earlier end of the inner?region radial flow of the whole system, the transition stage of radial flows will occur earlier, and the pressure derivative curve in the transition flow stage will change more slowly