A random four-parameter method is used to reconstruct pore structure of heterogeneous sandy conglomerate. Imbibition behavior of wetting fluid in porous media is studied with an improved SC-LBM (Shan-Chen lattice Boltzmann) model. It shows that interfacial dynamics at the initial stage is closely related to the arrangement of pore skeleton, and the imbibition interface is mainly formed by matrix. As fluid flows through the pore throat, the flow cross section shrinked instantly, leading to a rapid increase in pressure gradient and flow resistance. The presence of hole roar pressure leads to the flow cross section shrinked instantly, which increases the flow resistance, indicating that the change of pore radius has a great influence on imbibition rate. In the later stage, the wetting fluid forms a dominant imbibition channel, which reduces the swept area and greatly reduces the imbibition displacement rate. This study is helpful to understand the spontaneous imbibition of fluid in heterogeneous pores, and is of great significance to imbibition and oil displacement in fractured tight reservoirs.