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Porous media play a vital role in daily life and industrial production, but their flow resistance calculation is always a difficult at the same time a hot topic of research. In this paper, a tube-sphere combination model is established based on the actual porous media structure and flow characteristics. The model considers the flow resistance of porous media as the superposition of tube flow viscous resistance, the resistance of flowing around a small ball and through the variable diameter of a channel. From this, a new resistance equation without any empirical constant is derived. Based on 35 sets of experimental data collected from the literature, this paper compares and verifies the derived formula, the classical Ergun equation and the Carman equation under small Reynolds number. The experimental parameters include particle size range: 0.0375–56.8 mm; porosity range: 0.32–0.882; Reynolds number range: 0.006–10 730. It is found that in most cases, the derived formula has better adaptability than the Ergun equation and is equivalent to the prediction accuracy of the Carman formula in a Darcy regime. However, for the pre-Darcy regime with smaller Reynolds number, the experimental data itself are quite different, and the calculation results of the three formulas are quite different from the experimental value. The maximum error of the Ergun equation is 49%, that of the Kozeny–Carman equation is 39%, and that of the derivation equation is 37%, indicating that the region may have completely different resistance mechanisms.