Abstract This paper presents pressure bahavior of horizontal wells in dual-porosity, dual-permeability naturally fractured reservoirs. The proposed equation is obtained by double Fourier transformation and Laplace transformation. The results calculated for combinations of various dimensionless characterizing parameters, including the permeability ratio between matrix and fracture systems, have revealed the unique behavior of naturally fractured reservoirs when the flow state within the matrix blocks is taken into account. It is concluded that, for the flow within matrix blocks will weaken the essential nature of fluid flow through a dual-porosity, single permeability medium revealed by Warren-Root model. This paper also presents the application of "Tiab's Direct Synthesis" to horizontal wells in an infinite acting dual-porosity, dual-permeability naturally fractured reservoirs with pseudo-steady state interporosity flow.