The pore structure and unfrozen water film have a significant influence on the frost heave of saturated porous media. The freezing process and frost heaving characteristics of saturated sandstones have been studied in this research by theoretical and experimental approaches. A developed micromechanical model has been proposed, considering the distribution function of pore size, the effect of unfrozen water film, and the interfacial free energy. The distribution of pore size in sandstone can well satisfy a dual-pore structure model, including the thin pores and coarse pores. Besides, four typical thickness functions are used to investigate the influence of the thickness of unfrozen water film on the disjoining pressure and frost heaving strains. The exponential equation suggested by Fagerlund (1973) may be better to quantify the thickness of this film by comparing with the experimental results. In addition, the frost heaving strains are also very close to the experimental values if ignoring the unfrozen water film. This calculation results may give the reasons why a satisfactory results can also be obtained with the absence of the unfrozen water film in the previous models. This study provides a better understanding of the frost heaving mechanism of saturated porous materials.